Chore: Add config provider and legacy support for config management

[roguepikachu]

Description of your changes

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 make reviewable to ensure this PR is ready for review.
• Added backport release-x.y labels to auto-backport this PR if necessary.

How has this code been tested

Special notes for your reviewer

---

Summary by cubic

Add a new config provider to create, read, list, and delete configs stored as Kubernetes Secrets. Also adds legacy support so existing op-based workflows keep working.

• New Features

  • New internal provider: config with actions create/read/list/delete.
  • Stores configs in Secrets under key input-properties with labels:
    • config.oam.dev/catalog=velacore-config
    • config.oam.dev/type= (optional; list can filter by template)
    • CUE templates for both providers:
      • provider: "config" (new)
      • provider: "op" (legacy)
    • Registered in the compiler and legacy provider registry.

    • Migration

      • No changes required. Legacy op-based steps continue to work; new workflows can use provider "config".

    ^{Written for commit 7b3f5cd. Summary will update automatically on new commits.}

[codecov]

Codecov Report

❌ Patch coverage is 34.51327% with 148 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.78%. Comparing base (d7db9c4) to head (7b3f5cd).
⚠️ Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/providers/config/config.go	7.27%	102 Missing ⚠️
pkg/providers/legacy/config/config.go	59.29%	28 Missing and 18 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #222      +/-   ##
==========================================
+ Coverage   62.49%   68.78%   +6.29%     
==========================================
  Files          62       64       +2     
  Lines        4415     5235     +820     
==========================================
+ Hits         2759     3601     +842     
+ Misses       1324     1261      -63     
- Partials      332      373      +41     

Flag	Coverage Δ
e2etests	23.77% <34.51%> (?)
unit-test	61.81% <8.40%> (-0.68%)	⬇️

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