Add Dockerfile

The Dockerfile is used to build a Docker image with all MaxScale
dependencied included. A short readme for using the image is attached.

docker/config_extension_example.cnf

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+# Server definitions
+# Set the address of the server to the network address of a MySQL server.
+
+[server1]
+type=server
+address=127.0.0.1
+port=3306
+protocol=MySQLBackend
+
+# Monitor for the servers
+# This will keep MaxScale aware of the state of the servers.
+# MySQL Monitor documentation:
+# https://github.com/mariadb-corporation/MaxScale/blob/develop/Documentation/Monitors/MySQL-Monitor.md
+
+[MySQL-Monitor]
+type=monitor
+module=mysqlmon
+servers=server1
+user=myuser
+passwd=mypwd
+monitor_interval=1000
+
+# Service definitions
+# Service Definition for a read-only service and a read/write splitting service.
+
+# ReadConnRoute documentation:
+# https://github.com/mariadb-corporation/MaxScale/blob/develop/Documentation/Routers/ReadConnRoute.md
+
+[Read-Only-Service]
+type=service
+router=readconnroute
+servers=server1
+user=myuser
+passwd=mypwd
+router_options=slave
+
+# ReadWriteSplit documentation:
+# https://github.com/mariadb-corporation/MaxScale/blob/develop/Documentation/Routers/ReadWriteSplit.md
+
+[Read-Write-Service]
+type=service
+router=readwritesplit
+servers=server1
+user=myuser
+passwd=mypwd
+max_slave_connections=100%
+
+# Listener definitions for the services
+# Listeners represent the ports the services will listen on.
+
+[Read-Only-Listener]
+type=listener
+service=Read-Only-Service
+protocol=MySQLClient
+port=4008
+
+[Read-Write-Listener]
+type=listener
+service=Read-Write-Service
+protocol=MySQLClient
+port=4006