FileStore: add basic file storage API (#46051)

* #45498: fs API alpha

* #45498: remove grafanaDS changes for filestorage.go

* #45498: fix lint

* #45498: fix lint

* #45498: remove db file storage migration

* #45498: linting

* #45498: linting

* #45498: linting

* #45498: fix imports

* #45498: add comment

* remove StorageName abstractions

* FileStore: add dummy implementation (#46071)

* #45498: bring back grafanaDs changes, add dummy filestorage

* #45498: rename grafanaDs to public

* #45498: modify join

* #45498: review fix

* #45498:  unnecessary leading newline (whitespace) IMPORTANT FIX

* #45498: fix belongsToStorage

* #45498: fix removeStoragePrefix so that it works with abs paths

Co-authored-by: Ryan McKinley <ryantxu@gmail.com>

pkg/services/featuremgmt/registry.go

@@ -162,5 +162,11 @@ var (
 			Description: "Lock database during migrations",
 			State:       FeatureStateBeta,
 		},
+		{
+			Name:            "fileStoreApi",
+			Description:     "Simple API for managing files",
+			State:           FeatureStateAlpha,
+			RequiresDevMode: true,
+		},
 	}
 )