Add BundleNamespaceMapping generation

[Danil-Grigorev]

When a CAPI Cluster references a ClusterClass in a different namespace, a corresponding ClusterGroup is created in the Cluster namespace. This ensures that all clusters within the namespace sharing the same ClusterClass from other namespace are grouped together.

This ClusterGroup inherits ClusterClass labels, as well as applies two CAAPF specific labels to uniquely identify the group pointing to this ClusterClass in the cluster scope:

• clusterclass-name.fleet.addons.cluster.x-k8s.io: <class-name>
• clusterclass-namespace.fleet.addons.cluster.x-k8s.io: <class-ns>

Additionally, this configuration enables the creation of a BundleNamespaceMapping. The mapping selects all available bundles and establishes a link between the namespace of the Cluster and the namespace of the referenced ClusterClass. This allows Fleet Cluster to be evaluated as a target for application sources such as Bundles, HelmApps, or GitRepos, located in the ClusterClass namespace.

To configure this behavior, FleetAddonConfig should contain the following:

apiVersion: addons.cluster.x-k8s.io/v1alpha1
kind: FleetAddonConfig
metadata:
  name: fleet-addon-config
spec:
  cluster:
    applyClassGroup: true

Setting applyClassGroup: true ensures that Fleet automatically creates ClusterGroup object for Cluster resource and applies the necessary BundleNamespaceMapping for the cross-namespace bundle access.

Fixes #216