[FLINK-13553][qs] Add logging to AbstractServerHandler

Log every request on trace level.
Log caught exceptions in AsyncRequestTask.

flink-queryable-state/flink-queryable-state-client-java/src/main/java/org/apache/flink/queryablestate/network/AbstractServerHandler.java

@@ -110,6 +110,7 @@ public abstract class AbstractServerHandler<REQ extends MessageBody, RESP extend
 			final MessageType msgType = MessageSerializer.deserializeHeader(buf);
 
 			requestId = MessageSerializer.getRequestId(buf);
+			LOG.trace("Handling request with ID {}", requestId);
 
 			if (msgType == MessageType.REQUEST) {
 
@@ -263,6 +264,7 @@ public abstract class AbstractServerHandler<REQ extends MessageBody, RESP extend
 					write.addListener(new RequestWriteListener());
 
 				} catch (BadRequestException e) {
+					LOG.debug("Bad request (request ID = {})", requestId, e);
 					try {
 						stats.reportFailedRequest();
 						final ByteBuf err = MessageSerializer.serializeRequestFailure(ctx.alloc(), requestId, e);
@@ -271,6 +273,7 @@ public abstract class AbstractServerHandler<REQ extends MessageBody, RESP extend
 						LOG.error("Failed to respond with the error after failed request", io);
 					}
 				} catch (Throwable t) {
+					LOG.error("Error while handling request with ID {}", requestId, t);
 					try {
 						stats.reportFailedRequest();