[otlp] Remove Experimental Flag and emit stable Exception attributes by default

[rajkumar-rangaraj]

Fixes #4831
Design discussion issue #

This PR addresses the stabilization of exception attributes in the OpenTelemetry Semantic Conventions. With exception.type, exception.message, and exception.stacktrace now considered stable, the need for the OTEL_DOTNET_EXPERIMENTAL_OTLP_EMIT_EXCEPTION_LOG_ATTRIBUTES environment variable has been eliminated.

Changes

Please provide a brief description of the changes here.

• Removed the OTEL_DOTNET_EXPERIMENTAL_OTLP_EMIT_EXCEPTION_LOG_ATTRIBUTES environment variable.
• Ensured that exception.type, exception.message, and exception.stacktrace are automatically included in exports

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• [ ] Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6250307) 83.38% compared to head (72d49da) 83.12%.
Report is 31 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5258      +/-   ##
==========================================
- Coverage   83.38%   83.12%   -0.26%     
==========================================
  Files         297      271      -26     
  Lines       12531    11967     -564     
==========================================
- Hits        10449     9948     -501     
+ Misses       2082     2019      -63     

Flag	Coverage Δ
unittests	?
unittests-Solution-Experimental	83.11% <100.00%> (?)
unittests-Solution-Stable	82.85% <100.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...etryProtocol/Implementation/ExperimentalOptions.cs	100.00% <ø> (ø)
...rotocol/Implementation/OtlpLogRecordTransformer.cs	93.45% <100.00%> (ø)
...tation.AspNetCore/Implementation/HttpInListener.cs	89.72% <100.00%> (+0.14%)	⬆️
...AspNetCore/Implementation/HttpInMetricsListener.cs	89.47% <ø> (ø)
...plementation/HttpWebRequestActivitySource.netfx.cs	80.77% <100.00%> (ø)
...emetry/Metrics/Exemplar/SimpleExemplarReservoir.cs	80.43% <100.00%> (ø)

... and 34 files with indirect coverage changes

[Kielek]

🎉

[CodeBlanch]

Sent a nit on CHANGELOG but LGTM