Generic tendering_type field on the carrier core?

[ChrisNolan]

Many carriers have a "pickup type" / "dropoff type" option, which is currently hardcoded in a lot of places to just pick the default and ignore the option. #1095 allows the fedex specific ones to now be ShippingOptions for fedex specifically but it'll be easier for integrators who work with multiple carriers if there was a more generic representation of this. Similar to how the 'pickup request' does -- karrio decides on a few options, and those options can be mapped to the individual carrier specific options.

I think this is the better way to handle what was allowed in #195 and it could for example improve the hardcoding of Purolator's 'DropOff'/ 'PreSchedule' and dhl_poland_dropoff_type too and likely more.