[Feature] Allow friends of host to join private battles without a password

[jere0500]

Idea

I often play private games with close friends.
While it is easy for them to join via password. I find this process somewhat tedious.

Therefore, I would like to add a checkmark when requesting a private lobby.
It should bypass the need to enter the password for friends. Something similar to what was discussed here: #426

Progress

I have already written some simple code for it.

I am currently evaluating a way of implementing the necessary backend changes in the teiserver.