address the comment

Signed-off-by: Ryan Leung <rleungx@gmail.com>

client/client.go

@@ -71,6 +71,8 @@ type Client interface {
 	ScatterRegion(ctx context.Context, regionID uint64) error
 	// GetOperator gets the status of operator of the specified region.
 	GetOperator(ctx context.Context, regionID uint64) (*pdpb.GetOperatorResponse, error)
+	// ConfigClient gets the configuration client.
+	ConfigClient() ConfigClient
 	// Close closes the client.
 	Close()
 }
@@ -147,6 +149,10 @@ func NewClientWithContext(ctx context.Context, pdAddrs []string, security Securi
 	return c, nil
 }
 
+func (c *client) ConfigClient() ConfigClient {
+	return &configClient{c.baseClient}
+}
+
 type deadline struct {
 	timer  <-chan time.Time
 	done   chan struct{}