If write blocking is enabled, check the old source (new destination) to make sure that it still blocks writes. If it was not blocking writes, output a warning message, and block user writes on the cluster.

This should be done after we transfer the resume data from old destination to new destination. This ticket is a nice-to-have, but not necessary, guardrail, and we should evaluate whether to complete it once REP-30 is closer to wrapping.