Switch from deprecated public_builds to public_jobs in GitLab project client

## Summary
GitLab has deprecated the project field in favor of .

- Deprecated: `public_builds`— If true, jobs can be viewed by non-project members.
- Replacement: `public_jobs`— If true, jobs can be viewed by non-project members.
- Docs: https://docs.gitlab.com/api/projects/#create-a-project

## Code Reference
The client still appears to use at:
- https://github.com/crossplane-contrib/provider-gitlab/blob/master/pkg/namespaced/clients/projects/project.go#L312

## Requested Changes
- Update the GitLab client to use instead of for create/update operations.
- Review and update any related logic that reads/writes this field.
- Assess whether our public API/CRD should be adjusted:
- Option A: Soft transition — support both, prefer , and deprecate in our API with clear warnings.
- Option B: Hard transition — replace with and provide migration notes.
- Verify impacts on cluster resources and reconciliation behavior to avoid drift.

## Migration / Compatibility
- If changing CRD/API fields, provide upgrade notes and defaulting/translation where feasible.
- Add tests to cover creation/update with .

## Acceptance Criteria
- Client uses for project creation/update.
- Backward compatibility strategy is defined and documented.
- Tests updated/passing.