Add in payment method types to the tier. We've got payment methods on the PriceCurrency object, but we should add that to the tier as well. That's because the micro tiers cannot accept credit card (that 0.10, 0.25 and 0.50). This will enable Stuart to do a nice form in the devhub as per the mocks. A PriceCurrency is whats used in the actual payment flow and would override the Price object.
Please add STR here or mark it with [qa-] if no QA is needed.