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
```

app/import_functions.go

@@ -527,7 +527,10 @@ func (a *App) importUser(data *UserImportData, dryRun bool) *model.AppError {
 			}
 		}
 		if hasNotifyPropsChanged {
-			if savedUser, appErr = a.UpdateUserNotifyProps(user.Id, user.NotifyProps, false); appErr != nil {
+			if appErr = a.updateUserNotifyProps(user.Id, user.NotifyProps); appErr != nil {
+				return appErr
+			}
+			if savedUser, appErr = a.GetUser(user.Id); appErr != nil {
 				return appErr
 			}
 		}