Add API endpoint for issuing invoices

[michaeldzjap]

I am interested in using the invoice functionality. However, from looking at the defined routes I noticed that there doesn't seem to exist an API endpoint for issuing an invoice (the equivalent of /v1/wallet/owner/issue_send_tx say) only receiving. Would it be possible to add this?

[jaspervdm]

Unfortunately we don't have the full invoice support that grin has right now, however we are looking to add it shortly after v2.0.0 release.