feat: add Kubernetes probe aliases

[rustatian]

Reason for This PR

Support Kubernetes-style names for liveness and readiness probes.

Description of Changes

• Add /livez as an alias for /health and /readyz as an alias for /ready.
• Reuse the existing handlers to preserve plugin filters, responses, and shutdown behavior.
• Update the v3 documentation in docs: document v3 release and v6 plugins docs#80.

License Acceptance

By submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.

PR Checklist

• All commits in this PR are signed (git commit -s -S).
• The reason for this PR is clearly provided.
• The description of changes is clear and complete.
• Required documentation changes are included in docs: document v3 release and v6 plugins docs#80.
• Changelog entry: not applicable; this repository has no CHANGELOG.md.
• All added/changed functionality is tested.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.36%. Comparing base (171837d) to head (9f0067d).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #154   +/-   ##
=======================================
  Coverage   99.35%   99.36%           
=======================================
  Files           6        6           
  Lines         309      313    +4     
=======================================
+ Hits          307      311    +4     
  Misses          2        2           

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