This option has coredumpctl look at all journals instead of only the
local ones. This allows coredumpctl to show information about remote
coredumps if the coredumps are made available in /var/lib/systemd/coredump
and the corresponding journals are made available in /var/log/journal.
This is already possible using the --directory option but --all makes it
more user friendly since users don't have to enter the journal directory
anymore as long as it's available under /var/log/journal.
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