Add Preference for Zip Code

[rbebb]

Summary

We need to add a preference for setting the zip code. Currently, the user can only do this before compiling the app.

This will need to be accomplished with a geocoding service using a platform's location services or a geocoding service like Nominatim.

1. Location services option: https://pub.dev/packages/geolocator
2. Geocoding service option (review use policy): https://nominatim.org/

Definition of Done

• Preference for setting the zip code added