Description of problem:

The `fromClusterClaim` template function available in the policy framework generally allows for convenient access to certain properties of the cluster like the platform, or a cluster ID. However, some ClusterClaims are not always present, like the "hostedcluster.hypershift.openshift.io" property used in a fix for https://issues.redhat.com/browse/ACM-16141.

When the ClusterClaim does not exist, the policy will return a templating error, and not be able to evaluate the policy. The "default" template function can not even be used to get around this.

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

How reproducible:

Steps to Reproduce:

1. Create a policy with a template using something like `{{ 
   fromClusterClaim "foo.bar.io" }}`
2. Observe the error.
3. ...

Actual results:

Policy is non-compliant with a template error

Expected results:

The function could return an empty string, or a sentinel value, which would allow the policy author to determine how to deal with the situation.

In particular, the behavior of `fromClusterClaim` is different than the equivalent `lookup`: `{{ (lookup "cluster.open-cluster-management.io/v1alpha1" "ClusterClaim" "" "foo.bar.io").spec.value }}`, which would return a special empty value, allowing comparisons or defaulting behavior.

Additional info: