Adjust declarative config pojo toString, hashCode, equals to match autovalue

[jack-berg]

Resolve lingering TODOs from #8408

This has a number of benefits:

• Generated code is much shorter and more pleasant to read
• Get to remove a variety of warning suppresions @SuppressWarnings({"NullAway", "rawtypes", "BoxedPrimitiveEquality"})
• Consistent toString implementation with other value types in this repo. Notably, no inclusion of identity hashcode

To make sure the adjusted equals / hashcode implementations are correct, I've added ModelEqualsHasCodeTest. This uses reflection to detect all the model classes, then uses equalsverifier to assert correctness of equals and has code.

[codecov]

Codecov Report

❌ Patch coverage is 93.63439% with 117 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.94%. Comparing base (6d6bd70) to head (e79dfa3).

Files with missing lines	Patch %	Lines
...gure/declarativeconfig/model/AggregationModel.java	96.42%	1 Missing ⚠️
...declarativeconfig/model/AlwaysOffSamplerModel.java	87.50%	1 Missing ⚠️
.../declarativeconfig/model/AlwaysOnSamplerModel.java	87.50%	1 Missing ⚠️
.../declarativeconfig/model/AttributeLimitsModel.java	92.85%	1 Missing ⚠️
...clarativeconfig/model/AttributeNameValueModel.java	93.75%	1 Missing ⚠️
...eclarativeconfig/model/B3MultiPropagatorModel.java	87.50%	1 Missing ⚠️
...ure/declarativeconfig/model/B3PropagatorModel.java	87.50%	1 Missing ⚠️
...eclarativeconfig/model/BaggagePropagatorModel.java	87.50%	1 Missing ⚠️
...se2ExponentialBucketHistogramAggregationModel.java	93.75%	1 Missing ⚠️
...tiveconfig/model/BatchLogRecordProcessorModel.java	95.65%	1 Missing ⚠️
... and 107 more

Additional details and impacted files

@@              Coverage Diff              @@
##               main    #8526       +/-   ##
=============================================
+ Coverage     78.51%   90.94%   +12.42%     
- Complexity     8601    10208     +1607     
=============================================
  Files          1013     1013               
  Lines         29150    27166     -1984     
  Branches       3632     3181      -451     
=============================================
+ Hits          22887    24705     +1818     
+ Misses         5420     1734     -3686     
+ Partials        843      727      -116     

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