[otlp] Update changelog / Remove OtlpExporter resource modification code

[rajkumar-rangaraj]

Fixes #5927
Design discussion issue #

Changes

Please provide a brief description of the changes here.

• Updated changelog
• Removed OtlpExporter resource modification code

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 ✅

Project coverage is 86.50%. Comparing base (be82099) to head (3130b18).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6015      +/-   ##
==========================================
- Coverage   86.51%   86.50%   -0.02%     
==========================================
  Files         257      257              
  Lines       11699    11689      -10     
==========================================
- Hits        10121    10111      -10     
  Misses       1578     1578              

Flag	Coverage Δ
unittests-Project-Experimental	86.29% <100.00%> (+0.07%)	⬆️
unittests-Project-Stable	86.32% <100.00%> (-0.10%)	⬇️

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

Files with missing lines	Coverage Δ
...ation/Serializer/ProtobufOtlpResourceSerializer.cs	91.66% <100.00%> (+3.43%)	⬆️

... and 5 files with indirect coverage changes

[alanwest]

🥳