Ticket 49671 - Readonly replicas should not write internal ops to changelog
    
    Bug Description:  When a hub receives an update that triggers the memberOf
                      plugin, but that interal operation has no csn and that
                      causes the update to the changelog to fail and break
                      replication.
    
    Fix Description:  Do not write internal updates with no csns to the changelog
                      on read-only replicas.
    
    https://pagure.io/389-ds-base/issue/49671
    
    Reviewed by: simon, tbordaz, and lkrispen (Thanks!!!)