docs: fix broken relative links

[wuallen57730]

Why are these changes needed?

Five relative Markdown links in the docs don't resolve:

• docs/development/release.md points at ./helm-chart.md, but the file is at docs/release/helm-chart.md.
• docs/guidance/rayclient-nginx-ingress.md points at tls.md, which doesn't exist in this repo; the TLS guide now lives in the Ray docs.
• The two swagger-ui links in apiserver/README.md are missing the http:// scheme, so they render as relative paths. apiserver/DEVELOPMENT.md already writes the same two URLs correctly.
• apiserver/SecuringImplementation.md links to ../experimental/cmd/main.go, which was removed in delete unused experimental folder #4890. This was the last remaining reference to that folder.
• apiserver/DEVELOPMENT.md links to swagger-initializer.js.backup, which is generated by hack/update-swagger-ui.bash and is gitignored, so it is never in the tree. Changed to an inline code span.

Found by scanning every .md file for relative links that don't resolve.

Related issue number

N/A — doc link cleanup.

Labels

• If this PR has user-facing changes that require documentation updates at release time, I have added the doc-updates-required label.
• If this PR contains breaking changes, I have added the breaking-change label.

Checks

• I've made sure the tests are passing.
• Testing Strategy
  • Unit tests
  • Manual tests
  • This PR is not tested :(

Manual test instructions

Verified each link resolves after the change, and re-ran the relative-link scan over all .md
files.

[wuallen57730]

PTAL when you have a chance, thanks! cc @andrewsykim @rueian