Move Agent v3 Docs under NGINX One Console

[JTorreG]

Proposed changes

Moves the NGINX Agent v3 Documentation to be a part of the NGINX One Console docset.

Moves the v2 docs to the root of the NGINX Agent docset.

Adds a banner to the v2 Docs regarding v3 Availability and upgrade path

Checklist

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• I have read the contributing guidelines
• I have signed the F5 Contributor License Agreement (CLA)
• I have rebased my branch onto main
• I have ensured my PR is targeting the main branch and pulling from my branch from my own fork
• I have ensured that the commit messages adhere to Conventional Commits
• I have ensured that documentation content adheres to the style guide
• If the change involves potentially sensitive changes¹, I have assessed the possible impact
• If applicable, I have added tests that prove my fix is effective or that my feature works
• I have ensured that existing tests pass after adding my changes
• If applicable, I have updated README.md and CHANGELOG.md

Footnotes

1. Potentially sensitive changes include anything involving code, personally identify information (PII), live URLs or significant amounts of new or revised documentation. Please refer to our style guide for guidance about placeholder content. ↩

[github-actions]

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[ADubhlaoich]

Generally LGTM, though I have left a non-blocking suggestion on the topmost document about the content type argument.