CHORE: update CHANGELOG for v0.15.2

[pyansys-ci-bot]

Update CHANGELOG for v0.15.2 and remove .md files in doc/changelog.d.

Caution

Do not merge this pull request until the release has been successfully made.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.85%. Comparing base (9ba026c) to head (b2ad1eb).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5951   +/-   ##
=======================================
  Coverage   84.85%   84.85%           
=======================================
  Files         162      162           
  Lines       62548    62548           
=======================================
  Hits        53078    53078           
  Misses       9470     9470           

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