[release] Fix, update superset docs process (#8680)

Introduces some automation on superset doc's build using docker

RELEASING/Dockerfile.make_docs

@@ -0,0 +1,29 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You 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:3.6-jessie
+ARG VERSION
+
+RUN git clone --depth 1 --branch ${VERSION} https://github.com/apache/incubator-superset.git /superset
+WORKDIR /superset
+# install doc dependencies
+RUN pip install -r requirements.txt \
+    && pip install -r docs/requirements.txt
+# build the docs
+RUN python setup.py build_sphinx
+
+COPY make_docs_entrypoint.sh /entrypoint.sh
+ENTRYPOINT ["/entrypoint.sh"]