* Add Greenfield API endpoint for pull payment LNURL items
close#4365
* Rename GetLNURLs to GetPullPaymentLNURL
* update "ln-url-not-supported" to "lnurl-not-supported"
* remove hardcoding of "BTC"
* update "PullPayments_LNURL" to "PullPayments_GetPullPaymentLNURL"
* update description of 400 status code response
Co-authored-by: Nicolas Dorier <nicolas.dorier@gmail.com>
