Support custom field options ids

Purpose:
Update implementation of import users with custom fields is needed. It is related to adding unique identifiers to options in selectable fields (radio, single-select, multi-select).

Requirements:

1. Import custom field values by option names
2. If import batch contains options that are missing in custom field definition - update the custom field by adding missing options

Approach:

1. Option names should be replaced by option IDs when create/update user.
2. Consider using the same approach for updating custom fields, like updating departments