[repo] Add ReleaseNotes.md to include features shipped in stable release

[vishweshbankwar]

Fixes #
Design discussion issue #

Changes

Introduces a new file ReleaseNotes.md for adding the announcements related to the stable releases. This will help with easy access to information on new features added for that particular release. As an example, It's not obvious from the changelog that the exemplars support is now stable. ReleaseNotes.md will help with that.

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 86.35%. Comparing base (6250307) to head (915b469).
Report is 286 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5772      +/-   ##
==========================================
+ Coverage   83.38%   86.35%   +2.96%     
==========================================
  Files         297      256      -41     
  Lines       12531    11102    -1429     
==========================================
- Hits        10449     9587     -862     
+ Misses       2082     1515     -567     

Flag	Coverage Δ
unittests	?
unittests-Project-Experimental	86.17% <ø> (?)
unittests-Project-Stable	86.26% <ø> (?)
unittests-Solution	86.27% <ø> (?)
unittests-UnstableCoreLibraries-Experimental	85.86% <ø> (?)

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see 202 files with indirect coverage changes

[cijothomas]

Thank you!