Add an ability to disable/adopt LoadBalancer

[a13x5]

/kind feature

The problem

Currently when reconciling AWSCluster all resources needed for cluster to function are created. This works well when you have all nodes as instances. However this approach doesn't quite work when you have control plane inside kubernetes cluster (like in case of k0sproject/k0smotron).

When load balancer is managed externally it creates a conflict:

• CAPA controller creates LB and updates .spec.controlPlaneEndpoint of AWSCluster
• Hosted control plane provider creates LB by means of Kubernetes Service and updates .spec.controlPlaneEndpoint of AWSCluster

Since it's impossible to use CAPA without creating AWSCluster current work around is to put cluster.x-k8s.io/managed-by annotation and disable AWSCluster reconcile, which is suboptimal.

Desired solution

I see 2 ways to resolve this:

1. New id field is added to the AWSLoadBalancerSpec with an ability to adopt externally created LBs and thus skipping creation of the new LB.
2. New disableCreation field is added to the AWSLoadBalancerSpec which simply disables creation of LB completely.

This will allow to use CAPA in deployment scenarios where LB is managed externally.

[k8s-ci-robot]

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