[RELEASE] Release opentelemetry-cpp 1.28.0

[marcalff]

Fixes #4162

Changes

Please provide a brief description of the changes here.

• Release opentelemetry-cpp 1.28.0

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[marcalff]

Do not merge: waiting for CHANGELOG, and other PRs.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.78%. Comparing base (8e64695) to head (ecb6f3d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4233      +/-   ##
==========================================
- Coverage   82.79%   82.78%   -0.01%     
==========================================
  Files         415      415              
  Lines       17450    17450              
==========================================
- Hits        14446    14444       -2     
- Misses       3004     3006       +2     

see 1 file with indirect coverage changes

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