Move systemd-python to an optional logging subpackage
This avoids the need for libsystemd-dev when installing swh.core's cli component
Test Plan
tox
Migrated from D2149 (view on Phabricator)
Staging instance, all changes can be removed at any time
This avoids the need for libsystemd-dev when installing swh.core's cli component
tox
Migrated from D2149 (view on Phabricator)