Allow repaying in multiple times

This endpoint is dedicated to the creation of an installment plan as part of recollection strategy.
You'll need a recollection-case id to use this endpoint.

In the event of insolvency, your debtor can opt for an installment plan to repay his debt with smaller
recurring pamyents. This smoothens the repayment effort, allowing the debtor to reimburse selected
loans or bills progressively.

the value of the installment parameter must be obtained by calling the POST /installment-plan/compute
endpoint.

The repayment_method field allows you to decide between direct-debit and sepa credit transfer.
If you pick DIRECT_DEBIT, the debited account will reuse borrower's main repayment account.
cf. GET /borrower/{borrower_id}/repayment-methods endpoint

We know recollection process has costs, for this reason the recollection_fees field permits adding
an arbitrary amount to proposed installment plan. This amount can cover recollection expenses
for example. When recollection_fees are collected, they are paid-out to the partner later.