[Discussion] $QT_PLUGIN_PATH

I'm on NixOS. My host $QT_PLUGIN_PATH looks like this:

```
$ echo $QT_PLUGIN_PATH
/nix/store/fjkhr5kdp3lcb67jdwlh226mryahijls-plasma-workspace-6.5.5/lib/qt-6/plugins:/nix/store/110a5arwbz4fwhccvhac173cqf78c2qc-plasma5support-6.5.5/lib/qt-6/plugins:...
```

Distrobox forwards that env var to the containers, but those paths don't exist inside containers. This causes all Qt apps to crash, and to run them, I first need to `unset QT_PLUGIN_PATH`. Is there any reason Distrobox can't do this by default? (Looks like it would be done [here](https://github.com/89luca89/distrobox/blob/c6cc6a3d5bf541ebadd6fa64a0aaecb8292cea66/distrobox-enter#L442))