enable 'cluster-machines-ready' unit for workload clusters
!2032 (merged) added the 'cluster-machines-ready' unit, but only enabled it for the mgmt cluster
This MR enables it for the workload clusters as well, to avoid the detrimental side-effects of doing in parallel the CAPI node rolling update and the units upgrades.
(Contributes to mitigate #1157)
Edited by Thomas Morin