Adds 2.16 release notes

[DarshitChanpura]

Description

Adds 2.16 release notes.

Check List

• New functionality includes testing
• New functionality has been documented
• New Roles/Permissions have a corresponding security dashboards plugin PR
• API changes companion pull request created
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 65.27%. Comparing base (613aff1) to head (7f3b73e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4596      +/-   ##
==========================================
- Coverage   65.28%   65.27%   -0.02%     
==========================================
  Files         317      317              
  Lines       22272    22272              
  Branches     3582     3582              
==========================================
- Hits        14541    14538       -3     
- Misses       5939     5944       +5     
+ Partials     1792     1790       -2     

see 3 files with indirect coverage changes