chore: update CHANGELOG for v0.10.3

[pyansys-ci-bot]

Update CHANGELOG for v0.10.3 and remove .md files in doc/changelog.d.

Caution

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.38%. Comparing base (2431dfd) to head (d97bf6e).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1894   +/-   ##
=======================================
  Coverage   90.38%   90.38%           
=======================================
  Files         105      105           
  Lines        9330     9330           
=======================================
  Hits         8433     8433           
  Misses        897      897           

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