add delete tags operation"

src/operations/tags.gql

@@ -1,3 +1,7 @@
 mutation RetireTags($tagIds: [Int!]!) {
   retireTags(tagIds: $tagIds)
 }
+
+mutation DeleteTags($videoId: Int!, $tagsToDelete: [VideoTagInput!]!) {
+  deleteTags(videoId: $videoId, tagsToDelete: $tagsToDelete)
+}