add MultiError type (#2297)

errors/errors.go

@@ -160,3 +160,22 @@ func As(err error) (*Error, bool) {
 	}
 	return nil, false
 }
+
+func NewMultiError() *MultiError {
+	return &MultiError{
+		Errors: make([]*Error, 0),
+	}
+}
+
+func (e *MultiError) Append(err *Error) {
+	e.Errors = append(e.Errors, err)
+}
+
+func (e *MultiError) HasErrors() bool {
+	return len(e.Errors) > 0
+}
+
+func (e *MultiError) Error() string {
+	b, _ := json.Marshal(e)
+	return string(b)
+}