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/datasource/register.go

@@ -23,6 +23,7 @@ import (
 	datasource "github.com/grafana/grafana/pkg/apis/datasource/v0alpha1"
 	query "github.com/grafana/grafana/pkg/apis/query/v0alpha1"
 	"github.com/grafana/grafana/pkg/apiserver/builder"
+	grafanarest "github.com/grafana/grafana/pkg/apiserver/rest"
 	"github.com/grafana/grafana/pkg/plugins"
 	"github.com/grafana/grafana/pkg/promlib/models"
 	"github.com/grafana/grafana/pkg/registry/apis/query/queryschema"
@@ -151,6 +152,11 @@ func (b *DataSourceAPIBuilder) GetGroupVersion() schema.GroupVersion {
 	return b.connectionResourceInfo.GroupVersion()
 }
 
+func (b *DataSourceAPIBuilder) 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,
 		&datasource.DataSourceConnection{},
@@ -198,7 +204,7 @@ func (b *DataSourceAPIBuilder) GetAPIGroupInfo(
 	scheme *runtime.Scheme,
 	codecs serializer.CodecFactory, // pointer?
 	_ generic.RESTOptionsGetter,
-	_ bool,
+	_ grafanarest.DualWriterMode,
 ) (*genericapiserver.APIGroupInfo, error) {
 	storage := map[string]rest.Storage{}