feat: support optional infra cluster via feature flag

[phoban01]

Description

Support was added for the controlPlaneEndpoint field in #137.

This PR builds upon that work to support making the infrastructure cluster fully optional.

We do this by introducing a feature flag SkipInfraClusterPatch that when enabled will bypass patching of the infrastructure cluster.

[prometherion]

LGTM, it's something I was thinking of with that support.

May I ask you to commit some changes to enable this feature using env vars as we're doing with the external cluster reference?

cluster-api-control-plane-provider-kamaji/config/control-plane-components.yaml

Line 13480 in 5dc7d2b

- --feature-gates=ExternalClusterReference=${CACPPK_EXTERNAL_CLUSTER_REFERENCE:=false},ExternalClusterReferenceCrossNamespace=${CACPPK_EXTERNAL_CLUSTER_REFERENCE_CROSS_NAMESPACE:=false}

[phoban01]

@prometherion I've added the envvar to the manager.yaml.

I think control-plane-components.yaml should be generated/updated as part of a release right?

nvm, I see there's a CI check.

[prometherion]

Thanks, happy for the contribution, thanks a lot!