Add error status for Policy targetRefs targeting routing objects in different namespaces

[lgadban]

Gloo Edge Product

Open Source

Gloo Edge Version

v1.17+

Is your feature request related to a problem? Please describe.

Currently Kube Gateway Policies (e.g. RouteOptions, VHostOptions, etc.) cannot target routing objects (e.g. HTTPRoute, Gateway, etc.) across namespaces; that is, policy objects must live in the same namespace as the object they are targeting.
Adding support for this is tracked in #9832

As a user, you may not know this limitation, and If you attempt to target across namespaces, you get no feedback that this binding is not allowed. The only signal that the attachment was not successful is the lack of a status. This UX can be improved.

Describe the solution you'd like

We should add a status to policy objects to indicate that a cross-namespace binding was attempted and not successful

Describe alternatives you've considered

No response

Additional Context

When RefGrant support is added, the status should be updated to reflect that

See also:
https://github.com/solo-io/solo-projects/issues/6172
#9832

┆Issue is synchronized with this Asana task by Unito