EndpointSlice resources are tracked by Graph

[ja20222]

Currently, relationship.Capturer is used to determine if we need to process EndpointSlice resources

Because the Graph is a state of the Gateway API and relevant cluster resources, use it as a source to determine relevant 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 for EndpointSlice resources.