Use Connect RPC

Connect is an alternate implementation of gRPC. Since IO is written in Go, we are most interested in the Go implementation, connect-go . With aaecc6a , we switched to using Connect to communicate with Envoy. In 31d9804 , we switched to using Connect to call Google gRPC APIs. In c58be28 , we began using Connect to call OpenTelemetry gRPC APIs. Pros Connect is simple and well-tested, with many well-discussed advantages . Cons The Go gRPC library is supported by Google. Connect requires us to run our own code generation (but that's actually a preference ).