docs: publish v4 and v5 docs

[blakecduncan]

Pull Request Checklist

• Did you add new tests and confirm existing tests pass? (yarn test)
• Did you update relevant docs? (docs are found in the site folder, and guidelines for updating/adding docs can be found in the contribution guide)
• Do your commits follow the Conventional Commits standard?
• Does your PR title also follow the Conventional Commits standard?
• If you have a breaking change, is it correctly reflected in your commit message? (e.g. feat!: breaking change)
• Did you run lint (yarn lint:check) and fix any issues? (yarn lint:write)
• Did you follow the contribution guidelines?

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PR-Codex overview

This PR focuses on enhancing the workflow for generating and publishing versioned documentation for the aa-sdk, integrating support for both v4 and v5 documentation, and improving the preview functionality during pull requests.

Detailed summary

• Updated .gitmodules to include a new branch for docs-site.
• Modified .github/workflows/on-pull-request.yml to:
  • Set up versioned docs.
  • Generate and publish Fern docs.
  • Comment preview URLs in PRs.
• Created example workflows for versioned docs publishing and previewing.
• Added scripts for validating and debugging versioned docs setup.
• Enhanced setup-docs-versioned action for better version management.
• Implemented insert-docs-versioned.sh for managing documentation across versions.

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