feat: Add "what's new" sections to changelog

[klmcadams]

• Add the "what's new" sections to the changelog
  • Create the whatsnew.yml file containing new features for 0.11.x

Here's a picture of the what's new sidebar and the section within the changelog:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.30%. Comparing base (974b4d9) to head (80203f0).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1057   +/-   ##
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  Coverage   81.30%   81.30%           
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  Files          40       40           
  Lines        2755     2755           
=======================================
  Hits         2240     2240           
  Misses        515      515