chore: add header to owlbot config

Author: tswast

.github/.OwlBot.lock.yaml

@@ -1,3 +1,17 @@
+# Copyright 2021 Google LLC
+#
+# 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.
+
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-python:latest
   digest: sha256:a3a85c2e0b3293068e47b1635b178f7e3d3845f2cfb8722de6713d4bbafdcd1d