[kcms/users] Add fingerprint manager

As a start to improving the experience in Plasma with fingerprints, we can start by adding a fingerprint manager to the users kcm that communicates with fprint (https://fprint.freedesktop.org/fprintd-dev/).

Other projects needed for this to be useful:

• plasma/polkit-kde-agent-1 needs to actually tell the user to use their fingerprint, as even when the pam files are properly configured, it asks for a password (and doesn't accept it, waiting for the fingerprint)
• plasma/polkit-kde-agent-1 should support using the fingerprint and password at the same time
• sddm should support using the fingerprint and password at the same time https://github.com/sddm/sddm/pull/1220
• plasma/kscreenlocker should support using the fingerprint and password at the same time kscreenlocker!15 (closed) kscreenlocker!29 (closed) plasma-workspace!774 (closed)
• relevant pam files for adding fprintd need to be provided (possibly look at how GNOME does this)?

Current design for fingerprint manager:

Ideas:

• It may be a good idea to have managing of fingerprint hardware in a separate kcm
• fprint seems to only allow fingerprints to be named by their fingers (ex. left-thumb, right-index-finger, etc.), maybe there is a way to allow users to label the fingerprints themselves (useful if more than one person uses the computer)?
• It'd be nice to have this work in a mobile form factor, for future usage on Plasma Mobile