This makes the journaldriver configuration machine-independent.
The secret is loaded from agenix instead of being persisted on disk.
Change-Id: I592ae7f5726fcb7f37a406f69dcf5ac498eeb1b7
Reviewed-on: https://cl.tvl.fyi/c/depot/+/5302
Autosubmit: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
