Add authentication method for Gardener Shoot Clusters

[Avarei]

What problem are you facing?

I would like to manage freshly created Gardener Shoot Clusters in this provider. While Most Cluster Management Tools give a AdminKubeConfig, which can be used for setting up permissions for other users and groups - Gardener uses short lived AdminKubeConfigs that are made by creating a subresource on the Shoot Object in the “Seed” cluster.

How could Crossplane help solve your problem?

The Provider could use a Seed KubeConfig to dynamically request and cache the kubeconfig for a referenced shoot cluster.

I would love to implement and contribute this feature if you are open to it.