layered future: indicate whether a policy is implemented by the waypoint

**Describe the feature request**

Implementations with variance from stock MUST adopt the mechanism used by the Gateway API specification to indicate whether a policy is successfully implemented by a Waypoint. See [PolicyAncestorStatus](https://gateway-api.sigs.k8s.io/reference/spec/#gateway.networking.k8s.io/v1alpha2.PolicyAncestorStatus) and in particular [PolicyConditionReason](https://gateway-api.sigs.k8s.io/reference/spec/#gateway.networking.k8s.io%2fv1alpha2.PolicyConditionReason). For clarity stock OSS Istio will adopt the same mechanism and use the ACCEPTED state to indicate support for its own APIs.

**Describe alternatives you've considered**

**Affected product area (please put an X in all that apply)**

[ ] Configuration Infrastructure
[ ] Docs
[ ] Installation
[ ] Networking
[ ] Performance and Scalability
[X] Policies and Telemetry
[ ] Security
[ ] Test and Release
[ ] User Experience

**Additional context**
[Istio’s Layered Future, Policy and Conformance](https://docs.google.com/document/d/1fg95r3C8Iqyivs0OO3z7diiaL6SkD6Ke9SqxaufAVBQ/edit?usp=sharing)