#966 Feat(definitions): definition tabs, documentation, versions and CUE packages (14/21)

Stack 14/21 · after #965 · next #967

Targets main but builds on #965, so the earlier stack commits show here too: review the last commit only. Merge after #965.

Description of your changes

• Definitions are tabbed by type (Sources among them), each with Documentation, CUE Source and UI Schema tabs.
• A definition lists its revisions, and an application can pin a component, trait, policy or source to a version.
• Extensions lists the CUE packages definitions can import, built-in and custom.

Fixes #

I have:

• Read and followed KubeVela's contribution process.
• Related Docs updated properly. In a new feature or configuration option, an update to the documentation is necessary.
• Run yarn lint to ensure the frontend changes are ready for review.
• Run make reviewableto ensure the server changes are ready for review.
• Added backport release-x.y labels to auto-backport this PR if necessary.

Special notes for your reviewer

• The documentation comes from KubeVela's own reference generator (references/docgen), the one vela def doc-gen uses.