services: unattended-upgrade: Log output of the 'guix' commands.

Fixes <https://bugs.gnu.org/43011>.
Reported by Jesse Gibbons <jgibbons2357@gmail.com>.

Until now the stdout/stderr file descriptors were not redirected.

* gnu/services/admin.scm (unattended-upgrade-mcron-jobs)[code]: Remove
'with-logging' and use 'redirect-port' instead.