In order to ensure that gRPC-based clients can properly identify a maxWireVersion supported by the entire routing layer through a load balancer, the routers need to report it via the gRPC metadata. In order for the routing layer itself to report a consistent value, a wire version discovery mechanism needs to be implemented. See the design for more details: https://docs.google.com/document/d/1MoNt1rCEXrOZplNPQrnEYdBxIoqvSNvXUAts4z78cv8/edit#heading=h.gq89gct6uf3u