✨ Support override addon images by the cluster's annotation

[zhujian7]

Make the addon framework support override addon agents' images by the cluster's annotation.
If the managedCluster has annotation open-cluster-management.io/image-registries in format:

{
   "registries":[
      {
         "mirror":"quay.io/ocm/addon-examples",
         "source":"quay.io/open-cluster-management/addon-examples"
      }
   ]
}

For example:

apiVersion: cluster.open-cluster-management.io/v1
kind: ManagedCluster
metadata:
  annotations:
    open-cluster-management.io/image-registries: '{"registries":[{"mirror":"quay.io/ocm/addon-examples","source":"quay.io/open-cluster-management/addon-examples"}]}'

If the addon manager uses the GetAgentImageValues func in the addon manager like:

			addonfactory.GetAgentImageValues(
				addonfactory.NewAddOnDeploymentConfigGetter(addonClient),
				"global.imageOverrides.helloWorldHelm",
				"quay.io/open-cluster-management/addon-examples",
			),

and use the "global.imageOverrides.helloWorldHelm" placeholder in the agent manifests yaml like:

      - name: helloWorld-agent
        image: {{ .Values.global.imageOverrides.helloWorldHelm }}

The image will be overridden to "quay.io/ocm/addon-examples"

Note: if the addon is also configured by the addonDeploymentConfig to override the image, the addonDeploymentConfig will take precedence over this annotation.

[zhujian7]

/hold

[zhujian7]

/unhold
/assign @zhiweiyin318
/cc @qiujian16

[zhiweiyin318]

/lgtm

[qiujian16]

/approve
/lgtm

[openshift-ci]

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