Changes

docs(tekton): add README with v0 deprecation notice and update resource config mapping (#4310)

## Summary

This PR includes two main changes:

### 1. Updated resource-config mapping in fake GitHub triggers
- Changed resource-config map keys from full repository names
(`'org/repo'`) to short names (`'repo'`) in all fake GitHub trigger
files:
  - `fake-github-branch-push.yaml`
  - `fake-github-branch-push-single-platform.yaml`
  - `fake-github-pr.yaml`
  - `fake-github-pr-single-platform.yaml`
  - `fake-github-tag-create.yaml`
  - `fake-github-tag-create-single-platform.yaml`
- Updated lookup expression from `body.repository.full_name` to
`body.repository.name`
- **Note**: Filter lists still use full repository names as required for
proper GitHub event filtering

### 2. Added comprehensive README.md for tekton directory
- Created `tekton/README.md` with clear version information and
deprecation notice
- Documented that `v0/` is deprecated and `v1/` should be used for all
new development
- Added directory structure overview and key component descriptions
- Included development guidelines, common workflows, and resources
- Provides migration guidance from v0 to v1

## Why these changes?

1. **Resource config consistency**: Using short repository names
simplifies configuration and aligns with other parts of the CI system
2. **Documentation**: The tekton directory lacked a central README,
making it difficult for contributors to understand the structure and
versioning
3. **Deprecation clarity**: Explicitly marking v0 as deprecated helps
guide contributors to use the current v1 configurations

## Testing

- All trigger configurations have been validated for syntax correctness
- CEL expressions continue to work as expected
- No changes to actual resource values (timeouts, CPU, memory, etc.)

## Related Issues

N/A - These are maintenance improvements

## Checklist

- [x] Code follows the project's style guidelines
- [x] Documentation has been updated
- [x] Changes are backward compatible
- [x] No sensitive information is included in the changes

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
 (commit: dad2bbf)