Description of problem:
If image precaching enabled in CGU with ClusterVersion policies, TALO pod will crash with following trace in talo manager container logs:

2022-02-24T20:38:08.269Z	INFO	controllers.ClusterGroupUpgrade	[getClustersBySelectors]	{"clusterNames": ["helix21-0"]}
2022-02-24T20:38:08.269Z	INFO	controllers.ClusterGroupUpgrade	[getClustersNonCompliantWithPolicy]	{"policy: ": "du-upgrade-cluster-version-policy2", "clusters: ": ["helix21-0", "helix21-1", "helix21-2", "helix21-3"]}
panic: interface conversion: interface {} is nil, not map[string]interface {}

goroutine 661 [running]:
github.com/openshift-kni/cluster-group-upgrades-operator/controllers.(*ClusterGroupUpgradeReconciler).extractPrecachingSpecFromPolicies(0xc0007398c0, {0xc000517c00, 0x11}, 0xc000517c00, {0xc001132ba0, 0x2, 0x24a1ea0})
	/workspace/controllers/precache.go:348 +0xfea
github.com/openshift-kni/cluster-group-upgrades-operator/controllers.(*ClusterGroupUpgradeReconciler).precachingFsm(0xc0007398c0, {0x18c06b8, 0xc001131410}, 0xc000517c00)
	/workspace/controllers/precacheFsm.go:81 +0x14f
github.com/openshift-kni/cluster-group-upgrades-operator/controllers.(*ClusterGroupUpgradeReconciler).reconcilePrecaching(0xc0007398c0, {0x18c06b8, 0xc001131410}, 0xc000517c00)
	/workspace/controllers/precache.go:43 +0x12e
github.com/openshift-kni/cluster-group-upgrades-operator/controllers.(*ClusterGroupUpgradeReconciler).Reconcile(0xc0007398c0, {0x18c06b8, 0xc001131410}, {{{0xc00072a469, 0x7}, {0xc00072a434, 0xc}}})
	/workspace/controllers/clustergroupupgrade_controller.go:98 +0x26d
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).reconcileHandler(0xc0001e1f40, {0x18c0610, 0xc000adfa80}, {0x1541e40, 0xc0003df9e0})
	/go/pkg/mod/sigs.k8s.io/controller-runtime.3-0.20210709165254-650ea59f19cc/pkg/internal/controller/controller.go:298 +0x303
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).processNextWorkItem(0xc0001e1f40, {0x18c0610, 0xc000adfa80})
	/go/pkg/mod/sigs.k8s.io/controller-runtime.3-0.20210709165254-650ea59f19cc/pkg/internal/controller/controller.go:253 +0x205
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2.2()
	/go/pkg/mod/sigs.k8s.io/controller-runtime.3-0.20210709165254-650ea59f19cc/pkg/internal/controller/controller.go:214 +0x85
created by sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2
	/go/pkg/mod/sigs.k8s.io/controller-runtime.3-0.20210709165254-650ea59f19cc/pkg/internal/controller/controller.go:210 +0x354


Version-Release number of selected component (if applicable):
4.10 

How reproducible:
Always

Steps to Reproduce:
1. Apply a CGU with clusterversion policies and precaching enabled. 
2. Monitor CGU and TALO logs
3.

Actual results:
Precaching did not start. TALO pod in CrashLoopBackOff

Expected results:
Precaching ocp image started on selected spoke cluster


Additional info:
# CGU:
apiVersion: v1
items:
- apiVersion: ran.openshift.io/v1alpha1
  kind: ClusterGroupUpgrade
  metadata:
    annotations:
      kubectl.kubernetes.io/last-applied-configuration: |
        {"apiVersion":"ran.openshift.io/v1alpha1","kind":"ClusterGroupUpgrade","metadata":{"annotations":{},"name":"precache-ocp","namespace":"default"},"spec":{"clusters":["helix21-0"],"deleteObjectsOnCompletion":true,"enable":true,"managedPolicies":["du-upgrade-cluster-version-policy1","du-upgrade-cluster-version-policy2"],"preCaching":true,"remediationStrategy":{"maxConcurrency":2,"timeout":240}}}
    creationTimestamp: "2022-02-24T20:30:20Z"
    generation: 1
    name: precache-ocp
    namespace: default
    resourceVersion: "5178101"
    uid: 9fcdd2a5-a9a6-4686-86c2-b690200ef73d
  spec:
    clusters:
    - helix21-0
    enable: true
    managedPolicies:
    - du-upgrade-cluster-version-policy1
    - du-upgrade-cluster-version-policy2
    preCaching: true
    remediationStrategy:
      maxConcurrency: 2
      timeout: 240
  status:
    computedMaxConcurrency: 1
    precaching:
      spec: {}
    status: {}
kind: List
metadata:
  resourceVersion: ""
  selfLink: ""

# clusterversion PGT can be found here: 
http://registry.kni-qe-0.lab.eng.rdu2.redhat.com:3000/kni-qe/ztp-site-configs/src/87cd39a0e517f137ecaaf437a785a7d91985b326/policygentemplates/upgrade.yaml