* Alerting: PoC - default template in k8s templategroup API
* Move code to grafana/alerting
* Move validation to admission validation abstraction
* Testing
* Linting
* Workspace update
* Update grafana/alerting hash to the merged commit
* More user-friendly name and remove need for CREATE/UPDATE validation
Use __default__ for k8s object name and UID so that we don't need to restrict
CREATE/UPDATE for similarly named user-owned templates.
* create notifications module and generate models
* switch template group to app models
* switch time intervals to use app models
* switch receiver to use app models
* switch routing tree to use app models
* move schema registration to resource packages
* fix package names to match app
* fix codeowners
* fix UI to use metadata.name instead of uid
* update dockerfile
* move generated models to pkg
* remove provenance from field selector
* move client factories to test files
* rename GenericClient to TypedClient
