Dumps_v1: DRY up the parallel-rsync default arguments
All of our sync tasks use parallel-rsync to publish the generated dumps from the cephfs volume to the clouddumps100[1-2] servers. All of them share some common arguments.
We can cut down on repetition by defining these common arguments once and then referring to this definition in each of the dumps DAGs.
Some invocations have additional '--extra-args' parameters, but this option may be specified multiple times.
Bug: T388378