KIC: Introduce annotations available for gateway API resources

### Where is the problem?

https://docs.konghq.com/kubernetes-ingress-controller/latest/reference/annotations/

### What happened?

There is no introduction on annotations could be used on gateway API resources, such as `HTTPRoute` in the annotations page. Basically, `HTTPRoute` supports the same annotations as `Ingress`, but since some features like method match and header match are available in specs of `HTTPRoute`, so we disabled the annotations (when expression router enabled). We need to add introductions about the differences.

### What did you expect to happen?

There is a section to introduce annotations could be applied on gateway API resources like `HTTPRoute`.

### Code of Conduct and Community Expectations

- [X] I agree to follow this project's Code of Conduct
- [X] I agree to abide by the Community Expectations

Start with the annotations reference page at https://docs.konghq.com/kubernetes-ingress-controller/latest/reference/annotations/. Add a section covering annotations available on Gateway API resources such as HTTPRoute, including how they differ from Ingress annotations and which features are disabled when the expression router is enabled. Done means the page explains these differences clearly.

Written by the indexing model from the issue text.