Expected status condition when HTTPRoute parentRef Service type cannot be found

[conradhanson]

What would you like to be added:

We should add to conformance testing what the expected status condition(s) are when an HTTPRoute.spec.parentRefs specifies a Service type and it cannot be found. In Istio, we have this status condition defined as the following:

lastTransitionTime: <time>
message: 'parent service: "<service name>" not found'
reason: NoMatchingParent
status: "False"
type: Accepted

Also, we could set the the ResolvedRefs status condition to false with similar messaging as the Accepted condition. Example:

lastTransitionTime: <time>
message: 'parent service: "<service name>" not found'
reason: ResolvedRefs
status: "True"
type: ResolvedRefs
controllerName: <name of controller used>

Why this is needed:

This scenario (i.e. parent reference cannot be found) should have specific messaging to make the user aware of whether or not the HTTPRoute has been processed successfully.