Define standard PolicyAncestor status type for Policy objects #2923
Description
Spun out of #2813 (Specifically, #2813 (comment)).
What would you like to be added:
We need either an update to GEP-713, GEP-2648, and GEP-2649 or to make a small GEP under this issue to properly discuss the idea of a PolicyAncestorStatus field, as in BackendTLSPolicy.
The PolicyAncestorStatus field is a status field, based on the ParentStatus in Route objects, that describes its status relative to the named ancestor object. "Ancestor" is used instead of "Parent" (as in Route) because for Policy objects, the relevant object for status is not always going to be the targetRef of the Policy.
Why this is needed:
To further ease the use of the Policy Attachment API pattern.