MM-23395: Add websockets support for update group (#14202)

* MM-23395: add websockets support for update group

model/group.go

@@ -160,6 +160,11 @@ func (group *Group) IsValidForUpdate() *AppError {
 	return nil
 }
 
+func (group *Group) ToJson() string {
+	b, _ := json.Marshal(group)
+	return string(b)
+}
+
 var validGroupnameChars = regexp.MustCompile(`^[a-z0-9\.\-_]+$`)
 
 func (group *Group) IsValidName() *AppError {