⚠️ Clustectl v1alpha3 should block on v1alpha4 clusters

[fabriziopandini]

What this PR does / why we need it:
This is a backport of #4199

Cluster API v1alpha4 is introducing changes in how providers are deployed (see e.g webhooks running with manager).

As a consequence, clusterctl version v1alpha3 should not be allowed to run on v1alpha4 clusters

NB: While doing the change, also clusterctl version v1alpha3 should not be allowed to run on v1alpha2 clusters was implemented (this is not technically possible, but we are getting this for free while backporting), and tests are now refactored in order to make changes for supporting the next contract less invasive.

Which issue(s) this PR fixes:
Rif #4192

/milestone v0.3.x
/hold
for #4199 to merge

[fabriziopandini]

/test pull-cluster-api-test-release-0-3

[fabriziopandini]

/test pull-cluster-api-test-release-0-3

[k8s-ci-robot]

@fabriziopandini: The following test failed, say /retest to rerun all failed tests:

Test name	Commit	Details	Rerun command
pull-cluster-api-apidiff-release-0-3	2997f18	link	/test pull-cluster-api-apidiff-release-0-3

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

This pull-request has been approved by: vincepri

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[fabriziopandini]

@vincepri this is a backport of #4199 and we get this merged first 😅

[vincepri]

/hold cancel