Fix: Update APX default options to locate Distrobox in a different path

[nellfs]

The default path for the Distrobox curl installation is /usr/local/bin/distrobox, but the default APX config expects it to be at /usr/share/apx/distrobox/distrobox, this causes the APX to panic with the message: distrobox is not installed if the user tries to run without using the expected path.

A better approach seems to check in the PATH instead, and use it from there, so Distrobox would be found regardless of where it was installed.

[mirkobrombin]

At least in vanilla os, it should always give priority /usr/share/apx/distrobox/distrobox since we need to keep control over it. Maybe the $PATH can be used if that is not available.