trust some connections with unencrypted data

[totaam]

This check is hard-coding the socket types that can be trusted:

xpra/xpra/net/protocol/socket_handler.py

Lines 223 to 224 in 6f11298

	def is_sending_encrypted(self) -> bool:
	return bool(self.cipher_out_name) or self._conn.socktype in ("ssl", "wss", "ssh")

But there should be a way to override this and trust specific connections when the user knows that the transport used is actually safe.
Example use-cases:

• VMs running locally
• VPN connections
• connection to (local / DMZ) proxies that provide their own encryption

[totaam]

Done in the commit above.

Example usage:

xpra attach "tcp://192.168.0.10:10000/?trusted=yes"