Prior to this commit, the import was wrong since a new journal release changed
it.
This commit fixes that import (and bumps the journal requirements).
It also:
- adapts journal_client instantiation with the missing brokers, group_id, etc...
- add configuration checks on the journal client (+ tests)
Oh and this fixes the current ci build failure [1]
[1] https://jenkins.softwareheritage.org/job/DSEA/job/tests/260/console