Added EnvironmentFile to systemd unit (#3606)

* Added EnvironmentFile to systemd unit

* Added support for older releases

* Remove ARGS

* Fixed copy unit

* Fixed unit filename

* Update update.sh

x-ui.service.debian

@@ -0,0 +1,16 @@
+[Unit]
+Description=x-ui Service
+After=network.target
+Wants=network.target
+
+[Service]
+EnvironmentFile=-/etc/default/x-ui
+Environment="XRAY_VMESS_AEAD_FORCED=false"
+Type=simple
+WorkingDirectory=/usr/local/x-ui/
+ExecStart=/usr/local/x-ui/x-ui
+Restart=on-failure
+RestartSec=5s
+
+[Install]
+WantedBy=multi-user.target