OSRA-207 Add 'Payment Plan' to Sponsor

OSRA-207
You should still be able to use Capybara to select e.g. option with `value=""` and make sure that it's an unambiguous match - i.e. there is only one.

However, this feels to me as a job that a test - especially a Cucumber acceptance test - should not be called upon to perform. If there is a possibility that a selector can be generated with two identical options, something needs to be fixed in the code. If we start writing tests like this for every option of every selector, we'll never stop. The other point is also important - even though we do abuse our Cucumber features and use them to test our views, this particular test feels way too low-level. Is there no way to avoid duplicate options being a possibility?