VNC: Add SPICE as 2nd HTML5 option (in addition to existing noVNC; Java TigerVNC)

[lsthompson]

Describe the bug
Java VNC needs to go away to a distant land, forever.

To Reproduce
It still exists in the module as a dependency/function.

Expected behaviour
VNC should be via: noVNC (OK), SPICE (add) & XTerm.js (add)

Additional context
This improves security and increases compatibility. In 2023 it makes sense.
As we've overhauled noVNC in theory this process to +2 should be simpler now.

[Tftlegal]

Hi!
Unfortunately, I didn’t have the qualifications to make either noVNC or Java TigerVNC work from the client area of the panel. (Almost all of my hypervisors are behind NAT) Therefore, I decided that as an alternative option for client access, the container would use its own link to the PVE.
For example, to access the hypervisor https://192.168.8.1:8006 the link https://pve8.example.com will be used
Is it possible to add your own entry point from the admin panel? In my case, would it be convenient to add your own link along with the logo instead of a link in the menu for example Java TigerVNC? Or just the ability to add your own entry point. Thank you.