sync without fill owner by casdoor

[HRNasr]

1- Is it possible to sync the external database with the user table without choosing a tenant (owner)? We have to fill this field (owner) ourselves and not by the casdoor. This mode is helpful for merging multi-tenancy database with casdoor user databases and
2- sync with Custom where (not all data)

[casbin-bot]

@tangyang9464 @JalinWang @imp2002