// reconcileMachineRollingUpdate implements the rolling update strategy for the ControlPlaneMachineSet. It uses the
// indexed machine information to determine when a new Machine is required to be created. When a new Machine is required,
// it uses the machine provider to create the new Machine.
//
// For rolling updates, a new Machine is required when a machine index has a Machine, which needs an update, but does
// not yet have replacement created. It must also observe the surge semantics of a rolling update, so, if an existing
// index is already going through the process of a rolling update, it should not start the update of any other index.
// At present, the surge is limited to a single Machine instance.
//
// Once a replacement Machine is ready, the strategy should also delete the old Machine to allow it to be removed from
// the cluster.
//
// In certain scenarios, there may be indexes with missing Machines. In these circumstances, the update should attempt
// to create a new Machine to fulfil the requirement of that index.