feat: add droneci runner

- ensure /data and docker are available
- add droneci runner configuration

modules/droneci/templates/droneci_runner_service.erb

@@ -0,0 +1,20 @@
+[Unit]
+Description=Drone CI Runner
+After=docker.service
+Requires=docker.service
+
+[Service]
+ExecStart=/usr/bin/docker run --rm \
+  --name=drone-runner \
+<% @ports.each do |port| -%>
+  -p <%= port %> \
+<% end -%>
+<% @volumes.each do |volume| -%>
+  --mount <%= volume %> \
+<% end -%>
+  --env-file <%= @env_file %> \
+  <%= @docker_image %>
+Restart=always
+
+[Install]
+WantedBy=multi-user.target