Enable VNC debug logging

When setting `window.debugging = "vnc"`, enable VncConsole's debug
logging. This is particularly helpful for logging console resize
requests from the client (Cockpit) as well as resize announcements from
libvirt.

https://issues.redhat.com/browse/RHEL-73808

src/components/vm/consoles/vnc.jsx

@@ -168,7 +168,7 @@ class Vnc extends React.Component {
                         encrypt={encrypt}
                         shared
                         credentials={credentials}
-                        vncLogging='warn'
+                        vncLogging={ window.debugging?.includes("vnc") ? 'debug' : 'warn' }
                         onDisconnected={this.onDisconnected}
                         onInitFailed={this.onInitFailed}
                         additionalButtons={additionalButtons}