[pve-devel] (web) syslog: allow to select display date span

[Thomas Lamprecht]

This fixes a timeout which happens when the journal is really big
or/and lies on a slow disk. As journalctl per default reads everything.

As also a single boot may have a duration of over an year lets not use
a boot parameter (as in the previous spin of this series) but rather
the 'since', 'until' parameters from journalctl.

This only adds the UI for ext4, if the base concept is OK,
I'll make also those for ext6 and send them.

cheers,
Thomas