Why does `BusinessService` call non-public Java API to perform health check?

## Why you need it?
Is your feature request related to a problem? Please describe in details

- I noticed that `org.apache.seata.api.BusinessService` was calling a non-public Java API to do health checks. Refer to https://github.com/apache/incubator-seata-samples/blob/3ae0a30e94ccb76eabf8ffc15863dbfa29bda598/at-sample/at-api/src/main/java/org/apache/seata/api/BusinessService.java .

```java
import io.seata.core.exception.TransactionException;
import io.seata.core.rpc.netty.RmNettyRemotingClient;
import io.seata.rm.RMClient;
import io.seata.tm.TMClient;
import io.seata.tm.api.GlobalTransaction;
import io.seata.tm.api.GlobalTransactionContext;
import org.apache.seata.api.service.OrderService;
import org.apache.seata.api.service.impl.AccountServiceImpl;
import org.apache.seata.api.service.impl.OrderServiceImpl;
import org.apache.seata.api.service.impl.StorageServiceImpl;
import org.springframework.util.ReflectionUtils;

import java.lang.reflect.Method;
import java.sql.SQLException;
import java.util.concurrent.TimeUnit;

RmNettyRemotingClient rmNettyRemotingClient = RmNettyRemotingClient.getInstance();
Class rmRemoteClass = rmNettyRemotingClient.getClass();
ReflectionUtils.doWithFields(rmRemoteClass, field -> {
if (field.getName().equals("clientChannelManager")) {
field.setAccessible(true);
//channelManger
Object o = field.get(rmNettyRemotingClient);
Method reconnect;
try {
reconnect = o.getClass().getDeclaredMethod("reconnect", String.class);
reconnect.setAccessible(true);
reconnect.invoke(o, "my_test_tx_group");
} catch (Exception e) {
throw new RuntimeException("reconnect failed!", e);
}
}
});
```
- To do a health check, it is very strange to have to use reflection.

## How it could be?
A clear and concise description of what you want to happen. You can explain more about input of the feature, and output of it.

- No sure. Maybe expose the relevant API on the seata client side?

## Other related information
Add any other context or screenshots about the feature request here.

- Null.

Start with at-sample/at-api/src/main/java/org/apache/seata/api/BusinessService.java and trace the RmNettyRemotingClient and reflective clientChannelManager calls shown there. Determine the supported public API for the health check or reconnect behavior; done means BusinessService no longer requires reflective access and the intended behavior is documented by the sample.

Written by the indexing model from the issue text.