Add basic view to the settings page

This commit adds:
- a row to the settings page…
- …which links to a page explaining what basic view is

The new row (and link) will only appear for services who already have
the feature switched on. This is because we are not launching the
feature yet, so it shouldn’t be available to just anyone.

app/main/views/service_settings.py

@@ -635,6 +635,15 @@ def service_set_auth_type(service_id):
     )
 
 
+@main.route("/services/<service_id>/service-settings/set-basic-view", methods=['GET'])
+@login_required
+@user_has_permissions('manage_service')
+def service_set_basic_view(service_id):
+    return render_template(
+        'views/service-settings/set-basic-view.html',
+    )
+
+
 @main.route("/services/<service_id>/service-settings/letter-contacts", methods=['GET'])
 @login_required
 @user_has_permissions('manage_service', 'manage_api_keys')