lockscreen: implement authenticator switching

Harald Sitterrequested to merge
work/sitter/multiprompt into master

allows the user to select an authenticator (e.g. face or smart card) and authenticate using that instead of the regular pam configuration

By default this doesn't change the UX. The user has to enable the relevant kscreenlocker services via the config. After that new buttons appear for the various services. Clicking a button switches the active authenticator to that type.

Screenshot_20260813_113837

Part of kde-linux/kde-linux#665

Edited by Harald Sitter

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