bigtable/metricscaler: Add Dockerfile (#3103)

* bigtable/metricscaler: Add Dockerfile.
* Add copyright header

bigtable/metricscaler/Dockerfile

@@ -0,0 +1,24 @@
+# Copyright 2020 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.
+FROM python:3
+
+WORKDIR /usr/src/app
+
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY . .
+
+ENTRYPOINT [ "python", "./metricscaler.py"]
+CMD ["--help"]