lnrpc: enable RPC middleware in REST WebSockets

If we don't flag the /v1/middleware call as request streaming, it can't
be used properly with REST WebSockets because the proxy would close the
connection after the first request message.

lnrpc/metadata.go

@@ -13,6 +13,7 @@ var (
 		regexp.MustCompile("^/v1/channels/acceptor$"),
 		regexp.MustCompile("^/v1/channels/transaction-stream$"),
 		regexp.MustCompile("^/v2/router/htlcinterceptor$"),
+		regexp.MustCompile("^/v1/middleware$"),
 	}
 
 	// MaxGrpcMsgSize is used when we configure both server and clients to