What servers don't have good defaults these days, and what clients need any configuration at all beyond the username and password? I don't think this is true.
Also Snikket meets your Docker requirements if you're into containers.
The last time I tried to get jabberd set up on an Ubuntu install, the port-opening and config became a nightmare and induced me to give up. No good signal on why it wasn't working.
oh interesting, fair enough; I didn't know jabberd still existed! FWIW, Prosody, Ejabberd, OpenFire, etc. all mostly have sane defaults for a basic chat system (both in terms of performance and features). They won't be an exact match of course, but all the basic stuff should be there.
Also Snikket meets your Docker requirements if you're into containers.