use fix size threads pool (#3180)

Author: ivanmorozov333

ydb/core/protos/flat_scheme_op.proto

@@ -1019,6 +1019,9 @@ message TS3Settings {
     optional uint32 RequestTimeoutMs = 101;
     optional uint32 HttpRequestTimeoutMs = 102;
     optional uint32 ConnectionTimeoutMs = 103;
+
+    optional uint32 ExecutorThreadsCount = 104 [default = 32];
+    optional uint32 MaxConnectionsCount = 105 [default = 32];
 };
 
 message TTaskCleaner {

ydb/core/wrappers/s3_storage_config.cpp

@@ -107,10 +107,10 @@ Aws::Client::ClientConfiguration TS3ExternalStorageConfig::ConfigFromSettings(co
     if (settings.HasHttpRequestTimeoutMs()) {
         config.httpRequestTimeoutMs = settings.GetHttpRequestTimeoutMs();
     }
-    config.executor = std::make_shared<Aws::Utils::Threading::PooledThreadExecutor>(1);
+    config.executor = std::make_shared<Aws::Utils::Threading::PooledThreadExecutor>(settings.GetExecutorThreadsCount());
     config.enableTcpKeepAlive = true;
     //    config.lowSpeedLimit = 0;
-    config.maxConnections = 5;
+    config.maxConnections = settings.HasMaxConnectionsCount() ? settings.GetMaxConnectionsCount() : settings.GetExecutorThreadsCount();
     config.caPath = "/etc/ssl/certs";
 
     switch (settings.GetScheme()) {