Add sample docker-compose file with pulsar standalone (apache#2617)

Add sample compose file for experimentation purposes.

docker-compose/standalone-dashboard/README.MD

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+<!--
+
+    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.
+
+-->
+# Docker Compose
+
+In this folder path run the following command to start the cluster
+
+```
+docker-compose up
+```
+
+## Urls
+
+Assuming localhost the the following endpoint will be available
+
+
+[web-dashboard](http://localhost:80) pulsar admin dashboard, shows various metrics and metatdata information about the cluster
+
+[broker-admin](http://localhost:8080) access broker rest  interface
+
+[broker-service-url](pulsar//:locahost:6650)  broker service url for use with producers and consumers
+
+
+You can shut it down with the following command in folder path
+
+```
+docker-compose down
+```

docker-compose/standalone-dashboard/docker-compose.yml

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+#
+# 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.
+#
+
+version: '2'
+
+services:
+
+  standalone:
+    image: apachepulsar/pulsar
+    expose:
+      - 8080
+      - 6650 
+    environment:
+      - PULSAR_MEM=" -Xms512m -Xmx512m -XX:MaxDirectMemorySize=1g"
+    command: >
+      /bin/bash -c
+      "bin/apply-config-from-env.py conf/standalone.conf
+      && bin/pulsar standalone"
+
+  dashboard:
+    image: apachepulsar/pulsar-dashboard
+    depends_on:
+      - standalone
+    ports:
+      - "80:80"
+    environment:
+      - SERVICE_URL=http://standalone:8080