Unified QR: Enable request of JIT invoice

[danielnordh]

It would be helpful if ldkNode.unifiedQrPayment().receive had a parameter that could return a JIT version of the invoice.

Use case:

• User has insufficient receive capacity
• Developer can still use ldkNode.unifiedQrPayment().receive, but can get a JIT version back

This saves the developer creating individual addresses and then baking them into a unified QR themselves.