Store the state of `Fleet` feature flags in a `ConfigMap` with a configurable name

[Danil-Grigorev]

We need to define a path to specify applied feature flags externally from the CAAPF FleetAddonConfig resource.

This should allow to perform fleet chart patch tentatively based on the ConfigMap state for the upstream installation, and will not require to store state in condition, making it purely informational. It would also benefit rancher based installation, when the ConfigMap used is named rancher-config.

ConfigMap content should be in the form of:

apiVersion: v1
kind: ConfigMap
data:
  fleet: |
    extraEnv:
    - name: EXPERIMENTAL_OCI_STORAGE
      value: "true"

which would match rancher-config content expectations.

apiVersion: addons.cluster.x-k8s.io/v1alpha1
kind: FleetAddonConfig
metadata:
  name: fleet-addon-config
spec:
  config:
    featureGates:
      configMap:               # ConfigMap state configuration settings (optional)
        ref:                # Optional reference override. Can default to `cattle-fleet-system/fleet-flags`
          kind: ConfigMap
          apiVersion: v1
          name: rancher-config
          namespace: cattle-system
      experimentalOciStorage: true   # Enables experimental OCI storage support
      experimentalHelmOps: true      # Enables experimental Helm operations support