sd-bus: extend D-Bus authentication timeout considerably (#6813)

As it turns out the authentication phase times out too often than is
good, mostly due to PRNG pools not being populated during boot. Hence,
let's increase the authentication timeout from 25s to 90s, to cover for
that.

(Note that we leave the D-Bus method call timeout at 25s, matching the
reference implementation's value. And if the auth phase managed to
complete then the pools should be populated enough and mehtod calls
shouldn't take needlessly long anymore).

Fixes: #6418
(cherry picked from commit 036d61b3)
(cherry picked from commit 7f4b159f)