default_template_url removed from API controllers, causes PXE menu build failure
#4463 removed default_template_url methods from the two API controllers, but left it in the UI controller. This method is called by PXE default templates, e.g.
ks=<%= default_template_url(profile[:template], profile[:hostgroup]) %>
I see it's been fixed in the UI controller for the #4463 bug, but the code should have been moved somewhere common, not removed in 2/3 places.
failed to process template: undefined method `default_template_url' for #<Api::V2::ConfigTemplatesController:0x0000000a0ada48>
fixes #8228 - add a config_templates concern to serve config_templates controllers