event registration: support partial payments when constructing contribution
The contribution BAO add method supports two parameters that can be used to create a contribution with a partial payment: partial_payment_total and partial_amount_to_pay.
I'd like to modify CRM_Event_Form_Registration::processContribution() to add support for these parameters. Doing so would enable hook based modifications to pass a partial payment amount (e.g. to support a "deposit" amount on an event registration). There should be minimal impact on existing functionality as those params are not actively used. We would simply support them if they are passed to that function.
(looking for concept approval)