lib: Add service.proxy.getRunJournal()
lib: Add service.proxy.getRunJournal()

This returns the journal text for the current/recent service run,
similar to `systemctl status`. The output can be customized further by
the caller with additional options.

cockpit-project/cockpit,cockpit-project/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,martinpitt/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,mvollmer/cockpit,martinpitt/cockpit