[enhancement] Make WhoIs feature configurable (enabled/disabled)

[DragnEmperor]

The complete feature of WhoIs retrieval should be allowed to be enabled/disabled at organization and global level. This can be done via FallbackBooleanChoiceField](https://openwisp.io/docs/stable/utils/developer/custom-fields.html#openwisp-utils-fields-fallbackbooleanchoicefield).
Need to introduce checks like device.organization.is_whois_enabled wherever required.

Dependencies

• [feature] Add Whois model and basic functionality #1032
• [feature] Implement Celery task for WHOIS fetch based on device last IP #1033

[DragnEmperor]

I think we have a model AbstractOrganizationConfigSettings in which we can introduce this field is_whois_enabled