Modified updateUserNotifyProps to directly update the field (#18097)

* Modified updateUserNotifyProps to directly update the field

The method was only being used during import and it unnecessarily
made multiple queries to the DB.

Changed to a separate query that just updated the props field.

https://community-daily.mattermost.com/plugins/focalboard/workspace/zyoahc9uapdn3xdptac6jb69ic?id=285b80a3-257d-41f6-8cf4-ed80ca9d92e5&v=495cdb4d-c13a-4992-8eb9-80cfee2819a4&c=e4f9a891-85d6-4886-8590-1e327f7f8b8f

```release-note
NONE
```

* invalidating cache

```release-note
NONE
```

store/store.go

@@ -356,6 +356,7 @@ type PostStore interface {
 type UserStore interface {
 	Save(user *model.User) (*model.User, error)
 	Update(user *model.User, allowRoleUpdate bool) (*model.UserUpdate, error)
+	UpdateNotifyProps(userID string, props map[string]string) error
 	UpdateLastPictureUpdate(userID string) error
 	ResetLastPictureUpdate(userID string) error
 	UpdatePassword(userID, newPassword string) error