Unified Storage: Adds pruner to kv backend (#110549)

* WIP adding pruner to kv store impl

* pruner only keeps 20 most recent versions

* ignore grafana-kv-data folder

* extracts some stuff to pruner.go file. Adds tests. Adds kvBackendOptions.

* update logging, comments, exports kvbackendoptions fields

* update nooppruner ref

* fixes field casing in test

* fix test

* linter fixes

* remove comment

* make KvStorageBackend private

* Adds pruner key validation and tests. Fixes broken tests.

* update error message when validating pruner key

pkg/storage/unified/testing/storage_backend_test.go

@@ -18,7 +18,12 @@ func TestBadgerKVStorageBackend(t *testing.T) {
 		t.Cleanup(func() {
 			_ = db.Close()
 		})
-		return resource.NewKvStorageBackend(resource.NewBadgerKV(db))
+		kvOpts := resource.KvBackendOptions{
+			KvStore: resource.NewBadgerKV(db),
+		}
+		backend, err := resource.NewKvStorageBackend(kvOpts)
+		require.NoError(t, err)
+		return backend
 	}, &TestOptions{
 		NSPrefix: "kvstorage-test",
 		SkipTests: map[string]bool{