Service Attachment Type Missing From PolicyTargetReference Documentation

[danehans]

Bug description
The PolicyTargetReference API docs do not include a Service resource as a supported attachment type even though this type is reference in the Ambient Getting Started guide.

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

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

Expected behavior
The ability to reference a Service in an auth policy but according to the API docs only a Gateway is supported.

Steps to reproduce the bug
Use the example provided in https://istio.io/latest/docs/reference/config/security/authorization-policy/

Version (include the output of istioctl version --remote and kubectl version)
1.22

How was Istio installed?
istioctl install --set profile=ambient --skip-confirmation

Environment where bug was observed (cloud vendor, OS, etc)
kind cluster

Additionally, please consider attaching a cluster state archive by attaching
the dump file to this issue.