chore: update CHANGELOG for v0.11.21

[pyansys-ci-bot]

Update CHANGELOG for v0.11.21 and remove .md files in doc/changelog.d.

Caution

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

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.28% (target: -1.00%)	✅ ∅

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (4ba5fb0)	2537	2187	86.20%
Head commit (69c960d)	2537 (+0)	2194 (+7)	86.48% (+0.28%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#1206)	0	0	∅ (not applicable)

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

See your quality gate settings    Change summary preferences

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.48%. Comparing base (4ba5fb0) to head (69c960d).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1206      +/-   ##
==========================================
+ Coverage   86.20%   86.48%   +0.27%     
==========================================
  Files          39       39              
  Lines        2537     2537              
==========================================
+ Hits         2187     2194       +7     
+ Misses        350      343       -7     

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.