🌱 Move the ClusterTopologyReconciler to a separated package

[fabriziopandini]

What this PR does / why we need it:
This PR moves the ClusterTopologyReconciler to a separated package, separating it from the other controller that are stable.

NOTE: this PR is only re-shuffling things, no additional changes applied

Which issue(s) this PR fixes:
Fixes #5038

[fabriziopandini]

@killianmuldoon PTAL

[sbueringer]

/lgtm
(diffed all files to be sure, and it looks good)

[killianmuldoon]

I think we should rethink the clusterclass.go file as it doesn't make it clear what that functionality the file actually has. Could the getClass function be joined with currentstate.go? It seems that the functions fit well together.

Otherwise maybe it could be called classreader.go or something that titles what it does. Other than this I have no other nits.

[sbueringer]

One option could be to name it currentclusterclass analog to currentstate which signals a bit that we retrieve the current clusterclass/state in those files. But I have no strong opinion on that.

[k8s-ci-robot]

@fabriziopandini: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Rerun command
pull-cluster-api-apidiff-main	00556a3	link	/test pull-cluster-api-apidiff-main

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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[vincepri]

/approve
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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