feat(console): the VNC console uses the panel's own address

The console pages connect to /novncd/ on the address, scheme and port the
page itself was loaded from; nginx proxies it to novncd, which listens on
the loopback only. There is nothing to configure: the console works on
HTTPS (wss), behind another proxy and on any published port.

Before, the page connected to WS_PUBLIC_HOST/PORT/PATH, port 6080 by
default: straight to novncd, past nginx and without TLS, so an HTTPS panel
and a Docker container published on another port had no console until the
public port was set by hand, and novncd listened on every interface.

Gone: WS_PUBLIC_PORT, WS_PUBLIC_HOST, WS_PUBLIC_PATH and WS_CERT, the
installer's two public console questions and its 6080 firewall rule, the
Docker image's WS_PUBLIC_PORT and its init script lines, the manual
install's firewall rule for 6080 and nginx's unused /websockify location.
WS_HOST defaults to 127.0.0.1. A VM with a QEMU websocket port is still
reached on that port of the panel's host name (left for a separate
decision).

docker-compose.yml

@@ -15,9 +15,6 @@ services:
       # - SECRET_KEY=your-custom-secret-key-here
       # Optional: comma-separated trusted CSRF origins (e.g. http://wvc.example.com,https://wvc.example.com)
       # - CSRF_TRUSTED_ORIGINS=http://localhost,http://127.0.0.1
-      # The console goes through nginx on the panel's port: set this to the
-      # published port if it is not 80 (443 behind TLS)
-      # - WS_PUBLIC_PORT=443
       # Optional: PostgreSQL instead of the bundled sqlite (also WEBVIRTCLOUD_DB_PORT/_NAME/_USER)
       # - WEBVIRTCLOUD_DB_HOST=db.example.com
       # - WEBVIRTCLOUD_DB_PASSWORD=change-me