[ADMIN] Add FOSSA badges

[marcalff]

Fixes # (issue)

Changes

Please provide a brief description of the changes here.

• Add FOSSA badges in README.md

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

[netlify]

✅ Deploy Preview for opentelemetry-cpp-api-docs canceled.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.96%. Comparing base (b89e63c) to head (d8dd66d).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3280   +/-   ##
=======================================
  Coverage   87.96%   87.96%           
=======================================
  Files         205      205           
  Lines        6407     6407           
=======================================
  Hits         5635     5635           
  Misses        772      772