feat: implement dynamic branch based docs versioning

[Jaydeep869]

Description

This PR resolves #537 by introducing dynamic, branch based versioning for the Docusaurus documentation site.

As suggested in the issue, rather than relying on Docusaurus's default behavior (which permanently duplicates older docs entirely into the master branch and creates significant clutter over time), this approach allows maintaining older versions purely on remote Git branches named docs/X.Y.Z.

Changes made

1. Docusaurus Config: Enabled { type: 'docsVersionDropdown' } in docusaurus.config.js to render a native version dropdown for users to toggle.
2. Dynamic Build Script: Added a custom build hook build-versions.sh script that runs in CI. Before npm run build is called:
   • It scans for any branches matching docs/* (e.g. docs/0.7.0).
   • It uses git archive to pull only the documentation from those specific older branches.
   • It seamlessly injects them into the native Docusaurus versioned_docs/ folder right at build time.
   • Dynamically generates the required versions.json.

How to release a new version of docs going forward:

Whenever the maintainers want to snapshot a version (e.g., 0.6.0), all they have to do is check out the commit they want and run:
git checkout -b docs/0.6.0 && git push origin docs/0.6.0
The setup in this PR will then automatically include it in the version dropdown!

Fixes #537

Acceptance Criteria Met

• Docs changes if needed
• Testing changes if needed
• All workflow checks passing (automatically enforced)
• All review conversations resolved (automatically enforced)
• DCO Sign-off

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[manzil-infinity180]

i don't see any dropdown for version? could you send me video or ss?

[Jaydeep869]

hey @manzil-infinity180 I can see the version selector entry as Next in the docs navbar.
At the moment no semver docs branch (docs/X.Y.Z) exists in in-toto/witness yet, so only current docs are shown.
Once a branch like docs/0.1.0 is created in upstream, it will appear in the selector automatically.

Before

https://witness.dev/

After

https://deploy-preview-757--witness-project.netlify.app/