feat(poc): add schema form prototype with raw json fallback

[Baluduvamsi2006]

Why submit this pull request?

• Bugfix
• New feature provided
• Improve performance
• Backport patches

What changes will this PR take into?

This PR introduces a prototype (PoC) for schema-driven plugin configuration in APISIX Dashboard.

Summary

• Added a new Prototype Schema Form mode in the plugin editor drawer.
• Kept existing Raw JSON (Monaco) mode as fallback.
• Added mode switch to toggle between:
  • Prototype Schema Form
  • Raw JSON
• Implemented basic schema-to-form rendering support for:
  • string, number/integer, boolean
  • enum (select)
  • array<string> (tags input)
  • nested object
• Added initial conditional behavior support for:
  • if/then/else merge
  • basic dependencies (required propagation)
• Synced prototype form changes to JSON payload so users can verify/edit in Raw JSON mode.
• Added a safety guard for Monaco diagnostics setup to avoid runtime crashes when jsonDefaults is unavailable.

Why this approach

• Demonstrates feasibility of the GSoC schema-form idea with minimal risk.
• Maintains backward compatibility through JSON fallback.
• Enables incremental adoption and mentor/community review before full implementation.

Manual verification

• Opened plugin editor drawer.
• Edited fields in Prototype Schema Form and verified values appear in Raw JSON.
• Switched back and forth between modes without losing state.
• Saved plugin config successfully.

Related issues

refs #3347

Checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?
• Is this PR backward compatible? If it is not backward compatible, please discuss on the mailing list first