Follow-up for a109189fab
This follows the existing practice for
systemd-journal-{upload,gatewayd}.service,
as I think allocating a full-blown user
specifically for this purpose is an overkill.
And with DynamicUser=yes we can also take
advantage of implied sandboxing.
We already have some varlink support for the journal to perform
some actions like `Rotate`. It would be nice to be able to query
the journal via varlink too so this commit adds a new varlinkctl
based journal service that exposes a single GetEntries() call
to retrieve journal entries. Basic filtering is supported and
we can expand the API as needed.
This is a separate `io.systemd.JournalControl` [1] service from the
existing `io.systemd.Journald` to decouple read and write (thanks
to Lennart for suggesting this).
This also extracts some shared helper so that we do not duplicate
code when generating the json or when adding the filters.
[1] The name mirrors the bootctl->io.systemd.BootControl naming.
