Is it possible to serve AdminUI using a base url?

[vonba]

I'm in a scenario where Keystone needs to live in a sub directory, e.g. /backend

Currently I'm getting 404 errors for the Next JS chunks and also the Keystone API because everything is expected to live in the root.

It looked like Next itself has a config option to set baseUrl (I think that's what it's called), but I haven't been able to find this option in Keystone.

[pc-erin]

This seems to have been added by #8545