Delete a cluster on GKE via GitLab

Description

When we remove a cluster that has been created on GKE, we just remove the configuration on the GitLab side, but the cluster is left untouched on GKE.

We should provide a way to delete the cluster completely if users want to get rid of costs and don't use the GCP dashboard for that.

Proposal

Allow users to choose if they want to just remove the integration with a GKE cluster, or if they want to delete it permanently.

This includes also delete the ingress resources that will survive the cluster deletion

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