Fix missing gevent extra dependency in Docker setup (#7744)

* Fix missing `gevent` extra dependency in Docker setup

* Add missing ASF header

contrib/docker/Dockerfile

@@ -45,9 +45,10 @@ WORKDIR /home/superset
 
 COPY requirements.txt .
 COPY requirements-dev.txt .
+COPY contrib/docker/requirements-extra.txt .
 
 RUN pip install --upgrade setuptools pip \
-    && pip install -r requirements.txt -r requirements-dev.txt \
+    && pip install -r requirements.txt -r requirements-dev.txt -r requirements-extra.txt \
     && rm -rf /root/.cache/pip
 
 RUN pip install gevent

contrib/docker/requirements-extra.txt

@@ -0,0 +1,17 @@
+#
+# 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.
+#
+gevent==1.4.0