Add KafkaSinkV2 (#79)

* Add AppEventKafkaSink and AppEventKafkaSinkExtended for application-level metrics and custom metadata support

* Add AppEventKafkaSink and AppEventKafkaSinkExtended for application-level metrics and custom metadata support

* Standardised variable name

* Renamed customFields to appLabels to correctly identify in event

* Added applications start and end event in Kafka Sink

* Added applications start and end event in Kafka Sink

* Removed totalExecutorCount metric

* Removed successful metric from app_end

* Reverted KafkaSink to actual position and added new event class KafkaSinkV2, testcase and doc

---------

Co-authored-by: pp-achauhan <achauhan@pulsepoint.com>

Author: aashishchauhan06

docs/Flight_recorder_mode_KafkaSink.md

@@ -14,6 +14,28 @@ provided by the user. Use this mode to monitor Spark execution workload.
 Notes:
 - KafkaSink: the amount of data generated is relatively small in most applications: O(number_of_stages)
 - KafkaSinkExtended can generate a large amount of data O(Number_of_tasks), use with care
+
+## KafkaSinkV2 and KafkaSinkV2Extended
+
+**KafkaSinkV2** is an enhanced version of KafkaSink that adds application-level aggregated metrics and custom labels support.  
+It collects all stage/executor/query metrics from the base KafkaSink plus additional application lifecycle events and counters.  
+**KafkaSinkV2Extended** extends KafkaSinkV2 to also record detailed metrics for each executed Task.
+
+**Compatibility Note:** KafkaSinkV2 is backward compatible with KafkaSink in terms of configuration and basic event types.
+Existing consumers of KafkaSink events will continue to work as expected. KafkaSinkV2 adds two new event types
+(`applications_started` and `applications_ended`) with additional metadata that existing consumers can safely ignore
+if not needed.
+
+### Key Differences from KafkaSink
+
+1. **Application-Level Metrics:** KafkaSinkV2 emits `applications_started` and `applications_ended` events with aggregated counters
+2. **Custom Labels:** Support for custom metadata labels via `spark.sparkmeasure.appLabels.*` configuration
+3. **Enhanced Application End Event:** Includes executor counts, job/stage/task counters, and selected Spark configurations
+4. **Counter Tracking:** Tracks success/failure counts for jobs, stages, and tasks throughout application lifecycle
+
+## Configuration
+
+### KafkaSink / KafkaSinkExtended Configuration
 
 How to use: attach the KafkaSink to a Spark Context using the extra listener infrastructure. Example:
   - `--conf spark.extraListeners=ch.cern.sparkmeasure.KafkaSink`
@@ -40,6 +62,29 @@ Configuration - KafkaSink parameters:
        Example: --conf spark.sparkmeasure.kafka.ssl.keystore.location=/var/private/ssl/kafka.server.keystore.jks
 ```
 
+### KafkaSinkV2 / KafkaSinkV2Extended Configuration
+
+How to use: attach the KafkaSinkV2 listener to the Spark Context:
+
+```
+# Start the listener for KafkaSinkV2 (recommended):
+--conf spark.extraListeners=ch.cern.sparkmeasure.KafkaSinkV2
+
+# Or use KafkaSinkV2Extended for task-level metrics (generates more data):
+--conf spark.extraListeners=ch.cern.sparkmeasure.KafkaSinkV2Extended
+
+# Required Kafka configuration (same as KafkaSink):
+--conf spark.sparkmeasure.kafkaBroker = Kafka broker endpoint URL
+       Example: --conf spark.sparkmeasure.kafkaBroker=kafka.your-site.com:9092
+--conf spark.sparkmeasure.kafkaTopic = Kafka topic
+       Example: --conf spark.sparkmeasure.kafkaTopic=sparkmeasure-metrics
+
+# Optional - Custom application labels:
+--conf spark.sparkmeasure.appLabels.<labelKey> = Custom metadata value
+       Example: --conf spark.sparkmeasure.appLabels.project=my-project
+       Example: --conf spark.sparkmeasure.appLabels.environment=production
+```
+
 This code depends on "kafka-clients". If you deploy sparkMeasure from maven central,
 the dependency is being taken care of.
 If you run sparkMeasure from a jar instead, you may need to add the dependency manually
@@ -102,3 +147,32 @@ bin/spark-shell \
   "jobId" : "0",
   "appId" : "local-1660057441489"
 ...
+```
+
+**Note:** KafkaSinkV2 also emits all standard events like `stages_started`, `stages_ended`, `stage_metrics`, etc., 
+just like the original KafkaSink, ensuring backward compatibility.
+
+## Migration Guide: KafkaSink to KafkaSinkV2
+
+If you are currently using KafkaSink and want to migrate to KafkaSinkV2:
+
+1. **Configuration Change:** Simply replace the listener class name:
+   ```
+   # Old:
+   --conf spark.extraListeners=ch.cern.sparkmeasure.KafkaSink
+   
+   # New:
+   --conf spark.extraListeners=ch.cern.sparkmeasure.KafkaSinkV2
+   ```
+
+2. **Backward Compatibility:** All existing event types and their schemas remain unchanged. Your existing Kafka consumers will continue to work.
+
+3. **New Events:** KafkaSinkV2 adds two new event types (`applications_started` and `applications_ended`). If your consumers don't need these, they can simply ignore events with these names.
+
+4. **Optional Custom Labels:** Add custom labels for better filtering and organization:
+   ```
+   --conf spark.sparkmeasure.appLabels.project=my-project
+   --conf spark.sparkmeasure.appLabels.environment=staging
+   ```
+
+5. **Benefits:** You gain application-level aggregated metrics, custom labels, and selected Spark configurations without losing any existing functionality.

docs/Reference_SparkMeasure_API_and_Configs.md

@@ -433,6 +433,54 @@ This code depends on "kafka-clients", you may need to add the dependency explici
   --packages org.apache.kafka:kafka-clients:3.7.0
 ```
 
+## KafkaSinkV2 and KafkaSinkV2Extended
+
+```
+class KafkaSinkV2(conf: SparkConf) extends KafkaSink(conf)
+class KafkaSinkV2Extended(conf: SparkConf) extends KafkaSinkV2(conf)
+
+**KafkaSinkV2** is an enhanced version of KafkaSink that extends the SparkListener infrastructure
+with application-level aggregated metrics and custom labels support.
+
+Key Features:
+1. All stage/executor/query metrics from the base KafkaSink
+2. Application-level aggregated counters (executor/job/stage/task counts)
+3. Custom labels via spark.sparkmeasure.appLabels.* configurations
+4. Enhanced applications_started and applications_ended events with metadata
+5. Automatic capture of selected Spark configurations
+
+**Backward Compatibility:** KafkaSinkV2 emits all the same event types as KafkaSink,
+ensuring existing consumers continue to work. It adds two new event types that can be
+safely ignored by consumers that don't need them.
+
+How to use:
+*   --conf spark.extraListeners=ch.cern.sparkmeasure.KafkaSinkV2
+
+**KafkaSinkV2Extended** adds verbose task-level metrics (can generate O(Number_of_tasks) data)
+* How to use:
+*   --conf spark.extraListeners=ch.cern.sparkmeasure.KafkaSinkV2Extended
+
+Configuration - KafkaSinkV2 parameters:
+
+Required:
+--conf spark.sparkmeasure.kafkaBroker = Kafka broker endpoint URL
+       Example: --conf spark.sparkmeasure.kafkaBroker=kafka.your-site.com:9092
+--conf spark.sparkmeasure.kafkaTopic = Kafka topic
+       Example: --conf spark.sparkmeasure.kafkaTopic=spark-metrics
+
+Optional - Custom labels (recommended for filtering and organization):
+--conf spark.sparkmeasure.appLabels.<labelKey> = Custom metadata value
+       Example: --conf spark.sparkmeasure.appLabels.project=my-project
+       Example: --conf spark.sparkmeasure.appLabels.environment=production
+       Example: --conf spark.sparkmeasure.appLabels.team=data-engineering
+
+For detailed event schemas and examples, see:
+  - docs/Flight_recorder_mode_KafkaSink.md
+
+This code depends on "kafka-clients", you may need to add the dependency explicitly, example:
+  --packages org.apache.kafka:kafka-clients:3.7.0
+```
+
 ## Prometheus PushGatewaySink
 ```
 class PushGatewaySink(conf: SparkConf) extends SparkListener