federation: Allow a single ingress/egress gateway to be used for multiple ServiceMeshPeers

A user should be able to configure a single ingress and egress gateway that can be used for routing traffic from/to multiple peers.  Currently, users must use a singe pair of ingress/egress gateways for each peer, which requires the use of one load balancer per peer.

When trying to use a single set of federation ingress/egress gateways for connecting to two other meshes (ie creating two ServiceMeshPeer resources referencing the same gateways), service connections fail because of RBAC. We seem to create DENY AuthorizationPolicies that restrict the service port to exactly one remote workload identity, which breaks when you have two distinct identities that both should have access.