Remove requeues in DockerMachinePool implementation

[Jont828]

What would you like to be added (User Story)?

In #8842, we would ideally like to remove the need to requeue to check if all dependent objects are deleted, and the requeue to check if the DockerMachines are ready. Instead, we would like to set up a Watch() on DockerMachines and ensure they have an ownerRef to DockerMachinePools.

Detailed Description

N/A

Anything else you would like to add?

No response

Label(s) to be applied

/kind feature
One or more /area label. See https://github.com/kubernetes-sigs/cluster-api/labels?q=area for the list of labels.

[Jont828]

/assign @CecileRobertMichon

[sbueringer]

/triage accepted

[fabriziopandini]

/priority backlog
/remove kind-feature
/kind cleanup