Move lndhub invoice creation to service

app/services/lndhub_manager/create_user_invoice.rb

@@ -0,0 +1,13 @@
+module LndhubManager
+  class CreateUserInvoice < Lndhub
+    def initialize(user:, payload:)
+      @user = user
+      @payload = payload
+    end
+
+    def call
+      authenticate @user
+      addinvoice @payload
+    end
+  end
+end