[pi-hole] allow change of password

[dirstel]

pi-hole uses the password generated by umbrel. The password may be changed via shell-command, but app ignores this because auf the embedded parameter in the docer-compose.yaml. Setting a default password and allowing to change it would be preferred, so not any umbrel-user has complete access to pi-hole.

[al-lac]

As far as i have seen the password is unique per umbrel instance.

Of course it would be nice if changing the value would be possible. But this is something that is not possible now for all apps that have a default value set.