[skip ci]Fix golint warnings in errors (#9237)

Signed-off-by: Xiangyu Wang <xiangyu.wang@zilliz.com>

internal/util/milvuserrors/errors.go

@@ -17,40 +17,52 @@ import (
 )
 
 const (
-	MsgRootCoordNotServing  = "root coordinator is not serving"
+	// MsgRootCoordNotServing means that root coordinator not serving
+	MsgRootCoordNotServing = "root coordinator is not serving"
+	// MsgQueryCoordNotServing means that query coordinator not serving
 	MsgQueryCoordNotServing = "query coordinator is not serving"
-	MsgDataCoordNotServing  = "data coordinator is not serving"
+	// MsgDataCoordNotServing means that data coordinator not serving
+	MsgDataCoordNotServing = "data coordinator is not serving"
+	// MsgIndexCoordNotServing means that index coordinator not serving
 	MsgIndexCoordNotServing = "index coordinator is not serving"
 )
 
+// MsgCollectionAlreadyExist is used to construct an error message of collection already exist
 func MsgCollectionAlreadyExist(name string) string {
 	return fmt.Sprintf("Collection %s already exist", name)
 }
 
+// ErrCollectionAlreadyExist is used to construct an error of collection already exist
 func ErrCollectionAlreadyExist(name string) error {
 	return errors.New(MsgCollectionAlreadyExist(name))
 }
 
+// MsgCollectionNotExist is used to construct an error message of collection not exist
 func MsgCollectionNotExist(name string) string {
 	return fmt.Sprintf("Collection %s not exist", name)
 }
 
+// ErrCollectionNotExist is used to construct an error of collection not exist
 func ErrCollectionNotExist(name string) error {
 	return errors.New(MsgCollectionNotExist(name))
 }
 
+// MsgPartitionAlreadyExist is used to construct an error message of partition already exist
 func MsgPartitionAlreadyExist(name string) string {
 	return fmt.Sprintf("Partition %s already exist", name)
 }
 
+// ErrPartitionAlreadyExist is used to construct an error of partition already exist
 func ErrPartitionAlreadyExist(name string) error {
 	return errors.New(MsgPartitionAlreadyExist(name))
 }
 
+// MsgPartitionNotExist is used to construct an error message of partition not exist
 func MsgPartitionNotExist(name string) string {
 	return fmt.Sprintf("Partition %s not exist", name)
 }
 
+// ErrPartitionNotExist is used to construct an error of partition not exist
 func ErrPartitionNotExist(name string) error {
 	return errors.New(MsgPartitionNotExist(name))
 }