Re-examine org.fdo.AccountsService usage

[samcday]

Two known issues at present, which make me think we're not pawing at this service properly somehow:

• Sometimes the greetd user shows up in the user selection.
• systemd-homed users are not showing up

[samcday]

Guido dug up some relevant issues:

• https://gitlab.freedesktop.org/accountsservice/accountsservice/-/issues/89
• https://gitlab.gnome.org/GNOME/gdm/-/issues/732

[agx]

I think phrog does the equivalent of busctl call org.freedesktop.Accounts /org/freedesktop/Accounts org.freedesktop.Accounts ListCachedUsers to list users and that doesn't list homed users for me either (see above accountservice issue)