chore: update CHANGELOG for v0.13.0

[pyansys-ci-bot]

Update CHANGELOG for v0.13.0 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 89.31%. Comparing base (b9c6369) to head (7f2918e).
⚠️ Report is 2 commits behind head on main.

❌ Your project status has failed because the head coverage (89.31%) is below the target coverage (90.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2404      +/-   ##
==========================================
- Coverage   92.97%   89.31%   -3.67%     
==========================================
  Files         169      165       -4     
  Lines       11656    11582      -74     
==========================================
- Hits        10837    10344     -493     
- Misses        819     1238     +419     

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