Minor fixes before next release

[SkafteNicki]

What does this PR do?

Fixes

• Missing changelog entry
• Missing metric .rst file in docs
• Wrong rendering of headers, math and lists in some of the new clustering metrics
• Wrong examples for plotting multiple values

Before submitting

• Was this discussed/agreed via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

PR review

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in Github issues there's a high chance it will not be merged.

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📚 Documentation preview 📚: https://torchmetrics--2086.org.readthedocs.build/en/2086/

[codecov]

Codecov Report

Merging #2086 (6732f2f) into master (fe5f46f) will decrease coverage by 50%.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #2086     +/-   ##
========================================
- Coverage      87%     37%    -50%     
========================================
  Files         293     293             
  Lines       16304   16304             
========================================
- Hits        14182    6039   -8143     
- Misses       2122   10265   +8143