Support setting enable_geo_zone_* fields

[fho]

Make the enable_geo_zone_* writable:

• set computed to false
• when a pull zone type is 1(volume) the enable_geo_zone fields are irrelevant, the Get API will always return a true value for them, either add a validation rule that ensures that enable_geo_zone_fields can only bet set to true if type is=1, or ignore them somehow when type is 1
• in the admin panel there is only an option to enable the EU + US zone, the API has separate fields for it, that can also be set independently, when only enabling one of them the result shown in the webinterface is not clear, either combine them in terraform to also only have one EU+US geozone field or add a validation that both settings always needs to have the same values
• according to the admin panel, >=1 geozone must always be enabled, it's possible to disable all in the api though, add a validation for it
• add a testcase to set enable_geo_zone_* fields to false when type=0
• add a testcase that ensures that enable_geo_zone-* can only be true or are ignored when type is 1