Add getUsernames operation

src/operations/user.gql

@@ -37,3 +37,11 @@ query GetUserPlayTime($userId: Int!) {
     totalSeconds
   }
 }
+
+query getUsernames(
+  $matchString: String!
+  $limit: Int = null
+  $after: String = null
+) {
+  getUsernames(matchString: $matchString, limit: $limit, after: $after)
+}