Support KeePassXC CLI as master source

[kwin]

The CLI of KeePassXC supports emitting specific attributes of an entry from a Keepass DB via show (https://github.com/keepassxreboot/keepassxc/blob/develop/docs/man/keepassxc-cli.1.adoc#commands). That should be leveraged as master source.

[kwin]

Currently KeepassXC CLI does require to enter the password of the DB for each call (there is no cache). Reported in keepassxreboot/keepassxc#11746.