[#82259176] Past variant lookup improvements, capture_via_cc with amount

- Allow past variant lookup by pg_authorization_code
- `capture_via_cc` now requires an `amount` arg in case amount changes between auth/capture

Story: https://www.pivotaltracker.com/story/show/82259176

Assigned @dlinder 
This would be easier for me to read as individual assigns (in which case I suggest setting `data=form.cleaned_data`) or with the keys inlined in the comprehension, as both of those approaches clarify that match_keys has no purpose outside of the assign by totally eliminating the symbol.