[FIX] website_sale(_delivery): limit 'Setup payment / delivery methods' to group_system

When choosing a payment acquirer or a delivery provider there is a link
allowing to directly jump in the backend to configure them. It has been
introduced at 6c2535b9b6.

However it is displayed for every user going through the checkout process.
This commit limits it to group_system. It seems a better idea to not show
it to everyone as they don't have access to it anyway.

addons/website_sale/views/templates.xml

@@ -1417,6 +1417,7 @@
                                         </li>
                                     </ul>
                                     <a class="btn btn-default btn-block"
+                                            groups="base.group_system"
                                             t-attf-href="/web#return_label=Website&amp;action=#{payment_action_id}">
                                         <i class="fa fa-plus-square" aria-hidden="true"></i> Setup payment methods
                                     </a>

addons/website_sale_delivery/views/website_sale_delivery_templates.xml

@@ -47,6 +47,7 @@
                     </li>
                 </ul>
                 <a class="btn btn-default btn-block"
+                        groups="base.group_system"
                         t-attf-href="/web#return_label=Website&amp;action=#{delivery_action_id}">
                     <i class="fa fa-plus-square" aria-hidden="true"></i> Setup delivery methods
                 </a>