As survey owner I want to require payment from respondee

This could support a variety of ad-hoc payment cases, such as

* accommodation signup,
* partly subsidized products for event organizers (eg. organizer hoodies),
* partly subsidized tickets to an event for organizers (eg. TSH coniteanäytäntö),
* catch-all ”the financeperson said I need to pay XX € to the event, so please take my money” form
* etc.

Would require that the organization has a payment method configured.

When payments are configured for a Survey, it could automatically add a dimension for payment status (unpaid, paid, refunded).

Need to design how the price is calculated for a survey response:

* Easiest way would be to specify a fixed price per response. However, this would already fail to serve most obvious cases such as multiple products (better served by ticket shop?), several instances on one form submission etc.
* We could also assign prices to dimension values. This would, however, fail to serve multiple instances of a product.
* We could [embed a custom LISP dialect](https://github.com/con2/kirppu/blob/development/kirppu/provision_dsl/interpreter.py) or even WASM runtime for which we could compile pricing logic functions with Rust…
* …but let's not :)
* We could have a field type for product selection. Products and their prices would be configured via the configuration of that field type.

[Slack discussion](https://traconfi.slack.com/archives/C07NYB6LZJS/p1727438076807259) (`lippukauppa2025` private channel, ask Japsu)