Bootstrap fleet agent on the ClusterClass provisioned cluster

[Danil-Grigorev]

We need to add support for injecting agent installation using Cluster Class templating with topology mutation hook. To achieve
this, an extension config needs to be deployed. The should help with populating certificate into the manifest.

Initially, we can explore using generated cluster registration service account certificate for this purpose.

• Add cluster registration SA and secret for APIServerCA value defaulting
• Expose APIServerCA and APIServerURL in FleetAddonConfig CR to use in automatic install

Additionally, we need to deploy a backend that serves on endpoints exposed in the topology mutation hook. This backend should be able to support in-place patching for Kubeadm and RKE2 bootstrap templates.

• Implement topology mutating hook server.
• Implement topology mutating hook endpoints.
• Implement in-place patches for the bootstrap configuration.
• Support automatic templating for the fleet agent including required taint tolerations.