Add disable letsencrypt (#747)

Add NETBIRD_DISABLE_LETSENCRYPT support to explicit disable let's encrypt

Organize the setup.env.example variables into sections

Add traefik example

infrastructure_files/management.json.tmpl

@@ -21,8 +21,8 @@
         "TimeBasedCredentials": false
     },
     "Signal": {
-        "Proto": "http",
-        "URI": "$NETBIRD_DOMAIN:10000",
+        "Proto": "$NETBIRD_SIGNAL_PROTOCOL",
+        "URI": "$NETBIRD_DOMAIN:$NETBIRD_SIGNAL_PORT",
         "Username": "",
         "Password": null
     },