[otlp] OTLP Exporter Custom serializer - Spans

[rajkumar-rangaraj]

Fixes Part of #5730, Follow up #5916
Design discussion issue #

Changes

Please provide a brief description of the changes here.

TODO: Peer resolve, based on response from #5927 (comment)

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 90.85714% with 16 lines in your changes missing coverage. Please review.

Project coverage is 86.35%. Comparing base (6250307) to head (c25785d).
Report is 362 commits behind head on main.

Files with missing lines	Patch %	Lines
...entation/Serializer/ProtobufOtlpTraceSerializer.cs	90.80%	16 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5928      +/-   ##
==========================================
+ Coverage   83.38%   86.35%   +2.97%     
==========================================
  Files         297      261      -36     
  Lines       12531    11612     -919     
==========================================
- Hits        10449    10028     -421     
+ Misses       2082     1584     -498     

Flag	Coverage Δ
unittests	?
unittests-Project-Experimental	86.33% <90.85%> (?)
unittests-Project-Stable	86.28% <90.85%> (?)

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

Files with missing lines	Coverage Δ
...Implementation/Serializer/ProtobufOtlpTagWriter.cs	94.64% <100.00%> (ø)
...entation/Serializer/ProtobufOtlpTraceSerializer.cs	90.80% <90.80%> (ø)

... and 241 files with indirect coverage changes

[CodeBlanch]

LGTM