docs(ngf): add f5 metadata fields and improve page titles

[sankalpsthakur]

Proposed changes

Fixes nginx/nginx-gateway-fabric#5254

NGINX Docs headers now include f5-keywords, f5-description, and f5-summary for search and AI metadata. Most NGF pages were missing these fields, and several titles (for example ListenerSet API, UDPRoute, TCPRoute, Rate Limit Policy API) did not describe the guide outcome.

This PR:

• Adds f5-keywords, f5-description, and f5-summary to all content/ngf/** pages (landing, section indexes, and guides).
• Completes partial front matter on pages that already had only some of these fields.
• Expands non-descriptive titles into clearer, task-oriented titles, including:
  • ListenerSet API → Configure additional Gateway listeners with ListenerSet
  • UDPRoute / TCPRoute → Route UDP/TCP traffic with UDPRoute/TCPRoute
  • Rate Limit Policy API → Configure rate limiting with RateLimitPolicy
  • Similar updates for Client/Proxy/Upstream Settings Policy, Snippets, session persistence, permissions, and related pages

Body content and procedural steps are unchanged; this is front matter / title only.

Checklist

Before sharing this pull request, I completed the following checklist:

• I read the Contributing guidelines
• My branch adheres to the Git conventions
• My content changes adhere to the F5 Technical Writing Style Guide
• If my changes involve potentially sensitive information¹, I have assessed the possible impact
• I have waited to ensure my changes pass tests, and addressed any discovered issues

Validation

• Parsed YAML front matter for all 73 content/ngf Markdown files; each has non-empty f5-keywords, f5-description, and f5-summary.
• Spot-checked title length for newly expanded titles (kept under ~60 characters where practical).
• Docs-only change; no product code changes.

AI/LLM disclosure

• AI coding tools (including Grok and/or Codex agent-assisted editing) were used to help draft or modify code and this PR description.
• I reviewed the complete change, understand the reasoning, and ran the reported local tests before submitting.
• This submission is original work of authorship under the project CLA / contributor terms; AI output was not pasted unreviewed.

Note: F5 CLA may be required for external contributors; happy to complete the CLA bot prompt if it appears on this PR.

Footnotes

1. Potentially sensitive information includes personally identify information (PII), authentication credentials, and live URLs. Refer to the style guide for guidance about placeholder content. ↩

[github-actions]

✅ All required contributors have signed the F5 CLA for this PR. Thank you!
_{Posted by the CLA Assistant Lite bot.}

[sankalpsthakur]

I have hereby read the F5 CLA and agree to its terms

[sankalpsthakur]

recheck