Acceptance criteria:

• All tests related to storing and retrieving memberships work again
• Memberships have a payment ID for referencing payments

Implementation details:

Adapt LegacyConverters to use "get payment" use case from payments when transforming from Domain entities to legacy Doctrine entities. Mark as deprecated. The method needs a payment-specific handling:

• direct debit: use returned data to set fields (payment type, amount, interval) and merge the rest (iban, bic, legacy bank data) into the data blob.
• Remove paypal data handling
• Other payments not needed, since they are not implemented and don't have legacy data

Add payment ID to membership domain model and entity

Deprecate amount, interval and payment type in membership domain model

Remove all "incomplete" markers from tests in membership repository