Add `requiredDuringSchedulingRequiredDuringExecution` to ClusterResourcePlacement affinity

In ClusterResourcePlacement's affinity definitions, adding `requiredDuringSchedulingRequiredDuringExecution` would enable the scheduler to react to underlying changes to a member cluster over time that affect its ability to run certain workloads.

One concrete use case might be to ensure that workloads only run on clusters that contain GPU nodes. As nodes are added to and removed from a cluster, whether or not any GPU nodes exist in a cluster may change over time. As a cluster operator detects these changes and updates some label on the member clusters to indicate whether or not GPU nodes are available, Fleet would automatically reschedule workloads that require GPU nodes onto a different member cluster.