fix(cleanup): rare panic related to misuse of named return argument

```
panic: assignment to entry in nil map
goroutine 380 [running]:
github.com/werf/werf/pkg/cleaning/stage_manager.GetCustomTagsMetadata.func1({0xc000bee150?, 0x3cb2960?}, {0xc00177ee40?, 0xc000554d90?}, 0xc001414180, {0x0?, 0x0?})
    /git/pkg/cleaning/stage_manager/manager.go:160 +0x11e
github.com/werf/werf/pkg/storage/manager.(*StorageManager).ForEachGetStageCustomTagMetadata.func1({0x3cb2960, 0xc00177ee40}, 0x40761d?)
    /git/pkg/storage/manager/storage_manager.go:1042 +0xa5
```

Signed-off-by: Alexey Igrychev <alexey.igrychev@flant.com>

pkg/cleaning/stage_manager/manager.go

@@ -139,14 +139,14 @@ func (m *Manager) InitCustomTagsMetadata(ctx context.Context, storageManager man
 	return nil
 }
 
-func GetCustomTagsMetadata(ctx context.Context, storageManager manager.StorageManagerInterface) (stageIDCustomTagList map[string][]string, err error) {
+func GetCustomTagsMetadata(ctx context.Context, storageManager manager.StorageManagerInterface) (map[string][]string, error) {
 	stageCustomTagMetadataIDs, err := storageManager.GetStagesStorage().GetStageCustomTagMetadataIDs(ctx, storage.WithCache())
 	if err != nil {
 		return nil, fmt.Errorf("unable to get stage custom tag metadata IDs: %w", err)
 	}
 
 	var mutex sync.Mutex
-	stageIDCustomTagList = make(map[string][]string)
+	stageIDCustomTagList := make(map[string][]string)
 	err = storageManager.ForEachGetStageCustomTagMetadata(ctx, stageCustomTagMetadataIDs, func(ctx context.Context, metadataID string, metadata *storage.CustomTagMetadata, err error) error {
 		if err != nil {
 			return err