Use the latest Graph to determine if a resource triggers a Graph rebuild

[pleshakov]

Currently, relationship.Capturer is used to determine if we need to process Namespace or Endpointslice resources

Because the Graph is a state of the Gateway API and relevant cluster resources, use it as a source to determine relevant Namespace or Endpointslice resources, rather than a separate component. This will avoid having duplicated logic to track relationship and make the Graph the source of truth.

See FIXME https://github.com/nginxinc/nginx-kubernetes-gateway/blob/36d5df4f5b047eadcbc2b814f19c216a054c2d6c/internal/state/graph/graph.go#L51

Acceptance criteria:

• Use the Graph instead of relationship.Capturer

### Tasks
- [ ] https://github.com/nginxinc/nginx-gateway-fabric/issues/1263
- [ ] https://github.com/nginxinc/nginx-gateway-fabric/issues/1264