🌱 refactor failure domains logic out of controlplane internal package

[CecileRobertMichon]

What this PR does / why we need it:

What: In preparation for #3358, this PR moves the failure domains business logic out of controlplane/kubeadm/internal into util/. There should be no behavior changes as a result of this PR.
Why: Nothing in failure_domains.go, machine_filters.go and machine_collection.go is kubeadm or control plane specific. The logic should be available for reuse for other packages outside the KCP implementation.
How:

• controlplane/kubeadm/internal/failure_domain.go → util/failuredomains/failure_domains.go
• controlplane/kubeadm/internal/machine_collection.go → util/collections/machine_collection.go
• controlplane/kubeadm/internal/machinefilters/machine_filters.go → util/collections/machine_filters.go
• moved the global internal Log var to controlplane/kubeadm/internal/control_plane.go
• renamed FilterableMachineCollection to Machines
• changed PickMost signature (from func PickMost(c *ControlPlane, machines FilterableMachineCollection) *string to func PickMost(failureDomains clusterv1.FailureDomains, groupMachines, machines collections.Machines) *string) to allow make it generic, just like PickFewest (nothing in the func logic is control plane specific).

Note that none of these should be breaking changes as the modified code was previously part of the internal package which by Go convention cannot be imported.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Related to #3358

[vincepri]

/milestone v0.4.0

[fabriziopandini]

Thanks for this refactor @CecileRobertMichon !

Two nits not blocking and some question about machine_filters.go:

• does it makes sense to have machine filters a a separate package or should we merge machine filters into collections given that they are used together?
• should we leave KCP specific filters somewhere in KCP and move under util only generic machine filters (instead of moving everything)?

[fabriziopandini]

/lgtm

[CecileRobertMichon]

/approve

will follow up with #2062

[k8s-ci-robot]

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