problem: grpc upstream timeouts

solution: tune connection settings

src/main/kotlin/io/emeraldpay/dshackle/upstream/grpc/GrpcUpstreams.kt

@@ -57,6 +57,8 @@ class GrpcUpstreams(
         val channel: ManagedChannelBuilder<*> = if (auth != null && StringUtils.isNotEmpty(auth.ca)) {
             NettyChannelBuilder.forAddress(host, port)
                     .useTransportSecurity()
+                    .enableRetry()
+                    .maxRetryAttempts(3)
                     .sslContext(withTls(auth))
         } else {
             log.warn("Using insecure connection to $host:$port")
@@ -67,7 +69,7 @@ class GrpcUpstreams(
         val client = ReactorBlockchainGrpc.newReactorStub(channel.build())
         this.client = client
         var i = 0
-        val grpcExecutor = Executors.newFixedThreadPool(32) { r -> Thread(r, "grpc-up-$id-${i++}") };
+        val grpcExecutor = Executors.newFixedThreadPool(64) { r -> Thread(r, "grpc-up-$id-${i++}") };
         this.grpcTransport = EmeraldGrpcTransport.newBuilder()
                 .forChannel(client.channel)
                 .setObjectMapper(objectMapper)