HTTPRoute partial validity

As a user of NGF 
I want to know when my HTTPRoute is partially invalid
So that I can fix the issue.

A/C:
- Replace the TODO condition with the PartiallyInvalid condition on an HTTPRoute when one of the rules is invalid. 
- Resolve [FIXME](https://github.com/nginxinc/nginx-kubernetes-gateway/blob/52fab05f8455ad9d9c0f08a11c0dd6e992b5a797/internal/state/graph/httproute.go#L270)