A new conditions that informs if all tenants are usable #95

The existing AllTenantsReady condition will be "True" whenever all tenants are already in the condition "Ready", but may not have been upgraded (e.g. a new version just got ready before all the tenants were actually starting/set to be upgraded).

To resolve this, we need a new AllTenantsUsable condition, which would be a combination of latest version Ready + all relevant tenants Ready after that.