enable url setting in order to add Visit button in HA UI (#499)

Author: fthiery

common/rootfs/docker-entrypoint.sh

@@ -60,7 +60,7 @@ if bashio::config.true 'zigbee_herdsman_debug'; then
     export DEBUG="zigbee-herdsman:*"
 fi
 export NODE_PATH=/app/node_modules
-export ZIGBEE2MQTT_CONFIG_FRONTEND='{"port": 8099}'
+export ZIGBEE2MQTT_CONFIG_FRONTEND="{\"port\": 8099, \"url\": \"$(bashio::addon.ingress_entry)\"}"
 
 # Expose addon configuration through environment variables.
 function export_config() {