This is required in order to let password lookups work correctly when
shelling out to password-store from MSMTP, as it won't be calling
pinentry correctly otherwise.
The default `ivy-pass` function shells out to `pass` in such a way
that using pinentry with emacs doesn't work, causing EXWM to freeze
until `C-g` is hit, after which the password entry buffer pops up.
That was very inconvenient - however, the new auth-source integration
with pass works correctly and this commit introduces a new function
and bindings for using the same functionality as before but doing the
actual password-reading via auth-source.