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/services/apiserver/config.go

@@ -6,6 +6,8 @@ import (
 	"path/filepath"
 	"strconv"
 
+	playlist "github.com/grafana/grafana/pkg/apis/playlist/v0alpha1"
+	grafanarest "github.com/grafana/grafana/pkg/apiserver/rest"
 	"github.com/grafana/grafana/pkg/services/apiserver/options"
 	"github.com/grafana/grafana/pkg/services/featuremgmt"
 	"github.com/grafana/grafana/pkg/setting"
@@ -33,6 +35,7 @@ func applyGrafanaConfig(cfg *setting.Cfg, features featuremgmt.FeatureToggles, o
 	host := net.JoinHostPort(cfg.HTTPAddr, strconv.Itoa(port))
 
 	apiserverCfg := cfg.SectionWithEnvOverrides("grafana-apiserver")
+	unifiedStorageModeCfg := cfg.SectionWithEnvOverrides("unified_storage_mode")
 
 	o.RecommendedOptions.Etcd.StorageConfig.Transport.ServerList = apiserverCfg.Key("etcd_servers").Strings(",")
 
@@ -53,6 +56,9 @@ func applyGrafanaConfig(cfg *setting.Cfg, features featuremgmt.FeatureToggles, o
 	o.StorageOptions.StorageType = options.StorageType(apiserverCfg.Key("storage_type").MustString(string(options.StorageTypeLegacy)))
 	o.StorageOptions.DataPath = apiserverCfg.Key("storage_path").MustString(filepath.Join(cfg.DataPath, "grafana-apiserver"))
 	o.StorageOptions.Address = apiserverCfg.Key("address").MustString(o.StorageOptions.Address)
+	o.StorageOptions.DualWriterDesiredModes = map[string]grafanarest.DualWriterMode{
+		playlist.GROUPRESOURCE: grafanarest.DualWriterMode(unifiedStorageModeCfg.Key(playlist.GROUPRESOURCE).MustInt(0)),
+	}
 	o.ExtraOptions.DevMode = features.IsEnabledGlobally(featuremgmt.FlagGrafanaAPIServerEnsureKubectlAccess)
 	o.ExtraOptions.ExternalAddress = host
 	o.ExtraOptions.APIURL = apiURL