[otlp] Fix TODOs, Refactor Buffer Size Handling, and Cleanup Environment Variables

[rajkumar-rangaraj]

Fixes Part of #5730
Design discussion issue #

Changes

Please provide a brief description of the changes here.

• Fixed TODOs
• Moved the logic for increasing buffer size for logs and metrics to use shared functionality like traces.
• Updated method and variable names
• Removed the experimental environment variable as it is no longer required.

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

Attention: Patch coverage is 73.68421% with 10 lines in your changes missing coverage. Please review.

Project coverage is 86.33%. Comparing base (0c775e5) to head (670f614).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...ementation/Serializer/ProtobufOtlpLogSerializer.cs	44.44%	5 Missing ⚠️
...ntation/Serializer/ProtobufOtlpMetricSerializer.cs	44.44%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6009      +/-   ##
==========================================
+ Coverage   86.16%   86.33%   +0.16%     
==========================================
  Files         257      257              
  Lines       11690    11685       -5     
==========================================
+ Hits        10073    10088      +15     
+ Misses       1617     1597      -20     

Flag	Coverage Δ
unittests-Project-Experimental	86.27% <73.68%> (+0.49%)	⬆️
unittests-Project-Stable	86.22% <73.68%> (+0.15%)	⬆️

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

Files with missing lines	Coverage Δ
...lder/OpenTelemetryBuilderOtlpExporterExtensions.cs	100.00% <ø> (ø)
...etryProtocol/Implementation/ExperimentalOptions.cs	89.47% <ø> (+3.11%)	⬆️
...tation/ExportClient/Grpc/GrpcStatusDeserializer.cs	87.40% <100.00%> (+0.09%)	⬆️
...tation/OpenTelemetryProtocolExporterEventSource.cs	87.67% <100.00%> (+0.90%)	⬆️
...entation/Serializer/ProtobufOtlpTraceSerializer.cs	93.43% <ø> (+0.71%)	⬆️
...TelemetryProtocol/OtlpExporterOptionsExtensions.cs	96.90% <100.00%> (ø)
....Exporter.OpenTelemetryProtocol/OtlpLogExporter.cs	100.00% <100.00%> (+27.50%)	⬆️
...porter.OpenTelemetryProtocol/OtlpMetricExporter.cs	80.76% <100.00%> (+24.01%)	⬆️
...xporter.OpenTelemetryProtocol/OtlpTraceExporter.cs	89.28% <100.00%> (ø)
...ementation/Serializer/ProtobufOtlpLogSerializer.cs	95.41% <44.44%> (-3.77%)	⬇️
... and 1 more

... and 6 files with indirect coverage changes

[CodeBlanch]

LGTM