Add LndHub service, lnurl-pay endpoints

Enables the lnurl-pay payment workflow

app/models/user.rb

@@ -56,4 +56,10 @@ class User < ApplicationRecord
     self.valid?
     self.errors[attribute_name].blank?
   end
+
+  def ln_create_invoice(payload)
+    lndhub = Lndhub.new
+    lndhub.authenticate self
+    lndhub.addinvoice payload
+  end
 end