Logrotate jobs after 30 days by default

Lot of jobs do not discard their build history which is filling up the
disk on gallium (T91211). All of the jobs should have a day based
logrotation. Apply a 30 days policy on JJB defaults. Can still be
overriden on a per job basis using:

logrotate:

daysToKeep: xx

Bug: T91396
Change-Id: I33f51f3fdb2edaa0dae401382a8506bf2e6567f1