Missing reasons in the ResolvedRefs RouteConditionType documentation

[mlavacca]

What happened:
The ResolvedRefs Route condition (https://github.com/kubernetes-sigs/gateway-api/blob/main/apis/v1beta1/shared_types.go#L227-L234) documentation does not include the reasons InvalidKind and BackendNotFound among the possible ones that make it False.

What you expected to happen:

Since this godoc section's purpose is to enumerate the possible reasons that may lead to having one ConditionStatus instead of another, it is needed to ensure its exhaustivity. Hence, InvalidKind and BackendNotFound should be added to the possible reasons that can make the Accepted route condition False in the godoc section.

How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?: