Add OpenTelemetry baggage propagation

[Arnab Nandy (arnabnandy7)]

Issue describing the changes in this PR

Resolves #866

This PR adds worker-side support for OpenTelemetry Baggage propagation by:

• Adding the baggage map from language worker protobuf v1.13.0 to RpcTraceContext.
• Passing baggage received from the Functions host into ExecutionTraceContext.
• Exposing the baggage values through ExecutionTraceContext#getBaggage().
• Adding unit coverage for non-empty, empty, and null baggage values.

Pull request checklist

• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• I have added all required tests (Unit tests, E2E tests)

Additional information

The public TraceContext interface in azure-functions-java-core-library does not currently expose a baggage accessor. A coordinated core-library update is required to add getBaggage() to the customer-facing API. Once that version is released, the worker dependency can be updated and ExecutionTraceContext#getBaggage() can explicitly override the interface method.

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