Fixes#46190
- Added a package init() to load the catalog from the embedded YAML
once.
- Init() now no longer runs any initialization logic just validation, so
it was renamed to Validate.
**Related issue:** Resolves#42887.
From Claude's audit:
```
[...]
Concerns worth addressing
A. Catalog drift is the real long-term risk. Today the yaml is curated.
If a future engineer adds (say) POST /users/api_only, PATCH /users/api_only/:id, POST /users/roles/spec,
POST /password_reset, or any session-issuing route, an allowlisted api_only user can clone themselves or
broaden a peer's allowlist.
Suggest a CI test that hard-fails if any of those route prefixes show up in api_endpoints.yml,
plus a comment at the top of the yaml listing the categories that must never be added (user/role/invite/password/session/SSO).
[...]
```
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **Tests**
* Added validation tests for API endpoint configuration to ensure
security compliance and proper detection of restricted endpoint
combinations.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
**Related issue:** Resolves#42883
Added a new premium GET /api/_version_/fleet/rest_api endpoint that
returns the contents of the embedded `api_endpoints.yml` artifact.
Juan Fernandez