Provisioning: delete secrets on repository deletion (#108113)

- Add hooks to git, github and github webhooks to remove the. 
- Implement deletion in secrets package.
- Add `Mutator` interface and hooks so that we can register any mutator. 
- Add unit test coverage to those mutators. 
- Move provider specific mutation from the massive `register.go` to the respective packages (e.g. `git` , `github`, etc). 
- Add integration test for removal. 
- Change the decryption fallback to simply check for the repository prefix.

pkg/registry/apis/provisioning/extra.go

@@ -4,6 +4,7 @@ import (
 	"context"
 
 	provisioning "github.com/grafana/grafana/pkg/apis/provisioning/v0alpha1"
+	"github.com/grafana/grafana/pkg/registry/apis/provisioning/controller"
 	"github.com/grafana/grafana/pkg/registry/apis/provisioning/jobs"
 	"github.com/grafana/grafana/pkg/registry/apis/provisioning/repository"
 	"k8s.io/apiserver/pkg/authorization/authorizer"
@@ -13,12 +14,12 @@ import (
 
 type Extra interface {
 	Authorize(ctx context.Context, a authorizer.Attributes) (decision authorizer.Decision, reason string, err error)
-	Mutate(ctx context.Context, r *provisioning.Repository) error
 	UpdateStorage(storage map[string]rest.Storage) error
 	PostProcessOpenAPI(oas *spec3.OpenAPI) error
 	GetJobWorkers() []jobs.Worker
 	AsRepository(ctx context.Context, r *provisioning.Repository) (repository.Repository, error)
 	RepositoryTypes() []provisioning.RepositoryType
+	Mutators() []controller.Mutator
 }
 
 type ExtraBuilder func(b *APIBuilder) Extra