Let detekt check if the license is set on Kotlin files.

tools/detekt/license.template

@@ -0,0 +1,15 @@
+/\*
+ \* Copyright \(c\) 20\d\d New Vector Ltd
+ \*
+ \* Licensed under the Apache License, Version 2\.0 \(the "License"\);
+ \* you may not use this file except in compliance with the License\.
+ \* You may obtain a copy of the License at
+ \*
+ \*     http://www\.apache\.org/licenses/LICENSE-2\.0
+ \*
+ \* Unless required by applicable law or agreed to in writing, software
+ \* distributed under the License is distributed on an "AS IS" BASIS,
+ \* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied\.
+ \* See the License for the specific language governing permissions and
+ \* limitations under the License\.
+ \*/