Log workflow task duration with external storage metrics

[jmaeagle99]

What was changed

When a WFT takes longer than 5 seconds, emit a TMPRL1104 warn log with external storage data. Threshold can be configured via the TEMPORAL_WORKFLOW_TASK_DURATION_WARN_SECONDS environment variable.

Why?

Help customers better identify causes of long running workflow tasks.

Checklist

1. Closes SDK should log when WFT completion takes a long time - Java #2883

2. How was this tested: unit tests

3. Any docs updates needed? No

[cconstable]

WorkflowWorker also handles task failures and query responses but I don't think those are covered by this PR. Should those also update the PayloadUploadCount?

[cconstable]

Claude found a few things that seemed reasonable:

• The timer also covers the RespondWorkflowTaskCompleted call to the server. The existing WORKFLOW_TASK_EXECUTION_LATENCY metric does not. That may be intended, but it means the two numbers won't match. Worth a sentence in the doc comment.
• Setting the variable to 0 warns on every task, and there is no way to turn the warning off. Is that intended?