ServiceMeshGateway resource should be used to allow users to create a gateway in any project in the mesh.  It should allow the user to define all fields relevant for a gateway (e.g. v2.IngressGatewayConfig or v2.EgressGatewayConfig), as well as a reference to the governing control plane (although, this might be inferred based on which mesh the project is a member of; not sure how revisions/multiple control planes will affect this).