Cleanup of Countries and Regions List and Implementation of 2 Digit Country Codes

This has been discussed in the forums: https://forum.mautic.org/t/use-a-coherent-county-list-with-iso-abbreviations-in-db/10816.

It is very challenging to add a contact or company via API including a full address, because if country and state fields are not an exact match according to the Mautic regions definitions, the request gets rejected. As an aggravating factor, naming conventions on both country and region definitions are inconsistent, and regions of several countries are incomplete or outdated. Those issues are surely affecting geolocalization as well, since an exact match can hardly be guaranteed under such circumstances.

This project will see us determining an authoritative source for country and region references and implementing this across Mautic, ensuring that appropriate migrations are provided for existing users.