Update REST API reference to use stable template routes instead of preview #16813
Description
The REST API reference documentation for registry templates currently shows preview endpoints (/api/preview/registry/templates/*).
Templates were stabilized in CLI v3.194.0, and the CLI now uses stable endpoints at /api/registry/templates/*.
The documentation should be updated to reference the stable routes.
Location: content/docs/reference/cloud-rest-api/registry/
Related:
- Remove experimental flag requirement for registry operations pulumi#20361 (original stabilization attempt)
- Stabilize template registry operations pulumi#20458 (templates stabilization PR)
- [registry] Migrate CLI to use stable package endpoints instead of preview pulumi#21215 (CLI package migration)