handle rdp client connections

[totaam]

Stumbled upon some examples by accident as I was improving how we handle RDP clients wrongly connecting to an xpra server's TCP port: 91671a7

It should not be too hard to handle the very basic stuff (screen, mouse and keyboard), in a similar way to how we handle RFB connections: #3256

The difficult part is parsing the arcane X.224 packet format.

Code examples:

• aardwolf: https://github.com/skelsec/aardwolf/blob/main/aardwolf/network/x224.py
  and https://github.com/skelsec/aardwolf/blob/main/aardwolf/protocol/tpkt.py inspired by rdpy: https://github.com/citronneur/rdpy/blob/master/rdpy/protocol/rdp/x224.py
• https://github.com/FreeRDP/FreeRDP: https://github.com/FreeRDP/FreeRDP/blob/c13d4750f69e011104477da153c34c220aee2e4a/libfreerdp/core/tpdu.c

Docs:

• Protocol Examples
• Démystifier l'authentification RDP