clusterctl v1beta1 should allow upgrades starting from v1alpha3

[fabriziopandini]

Detailed Description

Considering the v1beta1 does not introduces breaking changes from v1alpha4, and that we want to allow a smooth migration towards v1beta1, then clusterctl v1beta1 should allow upgrades starting from v1alpha3

It is also required to have v1alpha3 --> v1beta1 and v1alpha4 --> v1beta1 (one of those is already there, but not working after breaking changes for v1beta1)

Anything else you would like to add:

The change requires to add v1alpha3 and v1alpha4 to allowed contracts in

cluster-api/cmd/clusterctl/client/upgrade.go

Lines 55 to 58 in d9db880

	// Ensure this command only runs against management clusters with the current Cluster API contract (default) or the previous one.
	if err := clusterClient.ProviderInventory().CheckCAPIContract(cluster.AllowCAPIContract{Contract: clusterv1old.GroupVersion.Version}); err != nil {
	return nil, err
	}

same for upgrade apply.

The E2E requires a dedicated prow job similar to https://github.com/kubernetes/test-infra/blob/f234f533b3e2ff5694e35b7a0c4466b4c7292042/config/jobs/kubernetes-sigs/cluster-api/cluster-api-periodics-main.yaml#L25-L59

But with:

• GINKGO_FOCUS targeting clusterctl upgrades (instead of GINKGO_SKIP)
• INIT_WITH_BINARY and INIT_WITH_KUBERNETES_VERSION

Most probably, also

cluster-api/test/e2e/clusterctl_upgrade.go

Lines 162 to 165 in 7084de3

	CoreProvider: input.E2EConfig.GetProvidersWithOldestVersion(config.ClusterAPIProviderName)[0],
	BootstrapProviders: input.E2EConfig.GetProvidersWithOldestVersion(config.KubeadmBootstrapProviderName),
	ControlPlaneProviders: input.E2EConfig.GetProvidersWithOldestVersion(config.KubeadmControlPlaneProviderName),
	InfrastructureProviders: input.E2EConfig.GetProvidersWithOldestVersion(input.E2EConfig.InfrastructureProviders()...),

should be changed to allow to pick a version from a specific release series (vs picking oldest).

/kind feature

[fabriziopandini]

/area clusterctl
/milestone v1.0
/kind release-blocking

[fabriziopandini]

/assign

[sbueringer]

Just fyi, testgrid looks like all tests are still consistently green.