Storage: Read desired mode from config instead of feature flags (#88353)

* Read desired mode from config
* Update playlist integration tests
* Add mode 1 playlist integration tests
* Add mode 0 dual writing to playlist integration tests
* Add documentation for the different dual writing modes

pkg/registry/apis/dashboardsnapshot/register.go

@@ -22,6 +22,7 @@ import (
 
 	dashboardsnapshot "github.com/grafana/grafana/pkg/apis/dashboardsnapshot/v0alpha1"
 	"github.com/grafana/grafana/pkg/apiserver/builder"
+	grafanarest "github.com/grafana/grafana/pkg/apiserver/rest"
 	"github.com/grafana/grafana/pkg/infra/appcontext"
 	"github.com/grafana/grafana/pkg/infra/db"
 	"github.com/grafana/grafana/pkg/infra/log"
@@ -86,6 +87,11 @@ func (b *SnapshotsAPIBuilder) GetGroupVersion() schema.GroupVersion {
 	return resourceInfo.GroupVersion()
 }
 
+func (b *SnapshotsAPIBuilder) GetDesiredDualWriterMode(dualWrite bool, modeMap map[string]grafanarest.DualWriterMode) grafanarest.DualWriterMode {
+	// Add required configuration support in order to enable other modes. For an example, see pkg/registry/apis/playlist/register.go
+	return grafanarest.Mode0
+}
+
 func addKnownTypes(scheme *runtime.Scheme, gv schema.GroupVersion) {
 	scheme.AddKnownTypes(gv,
 		&dashboardsnapshot.DashboardSnapshot{},
@@ -122,7 +128,7 @@ func (b *SnapshotsAPIBuilder) GetAPIGroupInfo(
 	scheme *runtime.Scheme,
 	codecs serializer.CodecFactory, // pointer?
 	optsGetter generic.RESTOptionsGetter,
-	dualWrite bool,
+	_ grafanarest.DualWriterMode,
 ) (*genericapiserver.APIGroupInfo, error) {
 	apiGroupInfo := genericapiserver.NewDefaultAPIGroupInfo(dashboardsnapshot.GROUP, scheme, metav1.ParameterCodec, codecs)
 	storage := map[string]rest.Storage{}