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).

.github/workflows/test.yml

@@ -197,7 +197,6 @@ jobs:
       - name: Console Through Nginx Only
         run: |
           [ "$(docker inspect -f '{{json .Config.ExposedPorts}}' webvirtcloud:ci)" = '{"80/tcp":{}}' ]
-          docker exec wvc grep -qx 'WS_PUBLIC_PORT = 80' /srv/webvirtcloud/webvirtcloud/settings.py
           code=$(curl -s -m 5 -o /dev/null -w '%{http_code}' -H 'Connection: Upgrade' -H 'Upgrade: websocket' \
             -H 'Sec-WebSocket-Version: 13' -H 'Sec-WebSocket-Key: dGVzdGtleXRlc3RrZXk9PQ==' http://127.0.0.1:8080/novncd/ || true)
           [ "$code" = 101 ] || { echo "websocket upgrade through nginx: $code"; exit 1; }