feat: Add systemd file and data to integrate the app as a daemon

data/systemd/before_253/revpi-middleware.service

@@ -0,0 +1,13 @@
+[Unit]
+Description=Middleware with D-Bus interface for Revolution Pi
+After=network.target
+
+[Service]
+EnvironmentFile=-/etc/default/revpi-middleware
+Type=notify
+NotifyAccess=all
+ExecStart=/usr/sbin/revpi-middleware $DAEMON_OPTS
+ExecReload=/bin/kill -HUP $MAINPID
+
+[Install]
+WantedBy=multi-user.target