Verify connection && Refactor async connection framework

iotdb-core/antlr/src/main/antlr4/org/apache/iotdb/db/qp/sql/IdentifierParser.g4

@@ -63,6 +63,7 @@ keyWords
     | CONDITION
     | CONFIGNODES
     | CONFIGURATION
+    | CONNECTION
     | CONNECTOR
     | CONTAIN
     | CONTAINS

iotdb-core/antlr/src/main/antlr4/org/apache/iotdb/db/qp/sql/IoTDBSqlParser.g4

@@ -64,7 +64,7 @@ ddlStatement
     | createContinuousQuery | dropContinuousQuery | showContinuousQueries
     // Cluster
     | showVariables | showCluster | showRegions | showDataNodes | showConfigNodes | showClusterId
-    | getRegionId | getTimeSlotList | countTimeSlotList | getSeriesSlotList | migrateRegion
+    | getRegionId | getTimeSlotList | countTimeSlotList | getSeriesSlotList | migrateRegion | verifyConnection
     // Quota
     | setSpaceQuota | showSpaceQuota | setThrottleQuota | showThrottleQuota
     // View
@@ -524,6 +524,10 @@ migrateRegion
     : MIGRATE REGION regionId=INTEGER_LITERAL FROM fromId=INTEGER_LITERAL TO toId=INTEGER_LITERAL
     ;
 
+verifyConnection
+    : VERIFY CONNECTION (DETAILS)?
+    ;
+
 // Pipe Task =========================================================================================
 createPipe
     : CREATE PIPE pipeName=identifier

iotdb-core/antlr/src/main/antlr4/org/apache/iotdb/db/qp/sql/SqlLexer.g4

@@ -165,6 +165,10 @@ CONFIGURATION
     : C O N F I G U R A T I O N
     ;
 
+CONNECTION
+    : C O N N E C T I O N
+    ;
+
 CONNECTOR
     : C O N N E C T O R
     ;

iotdb-core/confignode/src/main/java/org/apache/iotdb/confignode/client/ConfigNodeRequestType.java → iotdb-core/confignode/src/main/java/org/apache/iotdb/confignode/client/CnToCnNodeRequestType.java

@@ -19,7 +19,7 @@
 
 package org.apache.iotdb.confignode.client;
 
-public enum ConfigNodeRequestType {
+public enum CnToCnNodeRequestType {
   ADD_CONSENSUS_GROUP,
   NOTIFY_REGISTER_SUCCESS,
   REGISTER_CONFIG_NODE,
@@ -30,4 +30,6 @@ public enum ConfigNodeRequestType {
   STOP_CONFIG_NODE,
   SET_CONFIGURATION,
   SHOW_CONFIGURATION,
+  SUBMIT_TEST_CONNECTION_TASK,
+  TEST_CONNECTION,
 }

iotdb-core/confignode/src/main/java/org/apache/iotdb/confignode/client/DataNodeRequestType.java → iotdb-core/confignode/src/main/java/org/apache/iotdb/confignode/client/CnToDnRequestType.java

@@ -19,7 +19,7 @@
 
 package org.apache.iotdb.confignode.client;
 
-public enum DataNodeRequestType {
+public enum CnToDnRequestType {
 
   // Node Maintenance
   DISABLE_DATA_NODE,
@@ -35,6 +35,9 @@ public enum DataNodeRequestType {
   SET_CONFIGURATION,
   SHOW_CONFIGURATION,
 
+  SUBMIT_TEST_CONNECTION_TASK,
+  TEST_CONNECTION,
+
   // Region Maintenance
   CREATE_DATA_REGION,
   CREATE_SCHEMA_REGION,

iotdb-core/confignode/src/main/java/org/apache/iotdb/confignode/client/async/AsyncConfigNodeHeartbeatClientPool.java

@@ -22,17 +22,17 @@
 import org.apache.iotdb.common.rpc.thrift.TEndPoint;
 import org.apache.iotdb.commons.client.ClientPoolFactory;
 import org.apache.iotdb.commons.client.IClientManager;
-import org.apache.iotdb.commons.client.async.AsyncConfigNodeIServiceClient;
+import org.apache.iotdb.commons.client.async.AsyncConfigNodeInternalServiceClient;
 import org.apache.iotdb.confignode.client.async.handlers.heartbeat.ConfigNodeHeartbeatHandler;
 import org.apache.iotdb.confignode.rpc.thrift.TConfigNodeHeartbeatReq;
 
 public class AsyncConfigNodeHeartbeatClientPool {
 
-  private final IClientManager<TEndPoint, AsyncConfigNodeIServiceClient> clientManager;
+  private final IClientManager<TEndPoint, AsyncConfigNodeInternalServiceClient> clientManager;
 
   private AsyncConfigNodeHeartbeatClientPool() {
     clientManager =
-        new IClientManager.Factory<TEndPoint, AsyncConfigNodeIServiceClient>()
+        new IClientManager.Factory<TEndPoint, AsyncConfigNodeInternalServiceClient>()
             .createClientManager(
                 new ClientPoolFactory.AsyncConfigNodeHeartbeatServiceClientPoolFactory());
   }
@@ -53,7 +53,6 @@ public void getConfigNodeHeartBeat(
     }
   }
 
-  // TODO: Is the ClientPool must be a singleton?
   private static class AsyncConfigNodeHeartbeatClientPoolHolder {
 
     private static final AsyncConfigNodeHeartbeatClientPool INSTANCE =