feat: add amount to nut05

[thesimplekid]

In order to support paying an amount-less invoice, add amount to quote request.

• CDK Melt to amountless invoice cdk#497
• Nutshell [FEAT] Amountless Melt Requests nutshell#712
• Nutmix
• goNuts mint - support paying amountless invoices elnosh/gonuts#137

closes #172

[prusnak]

I think we should specify whether amount can be provided if bolt11 invoice contains an amount.

There are 3 options:
a) amount must not be provided
b) amount can be provided but is ignored
c) amount can be provided but must match the amount in bolt11 invoice

I like the C option the most.

[thesimplekid]

I think we should specify whether amount can be provided if bolt11 invoice contains an amount.

Good point, I've updated wording to reflect this.

[callebtc]

Setting for the info endpoint (some backends can't pay amountless invoices)

[thesimplekid]

Setting for the info endpoint (some backends can't pay amountless invoices)

Added in 6628ff1

[prusnak]

re-ACK after the new changes

[a1denvalu3]

Nutshell: cashubtc/nutshell#712

[elnosh]

gonuts: elnosh/gonuts#137
just pending resolution on the conflicting error codes with #223