Route entity.group_content_menu.add_link checks for group perm "create group_content_menu:default_group_menu content" that does not exist

Problem/Motivation

I need users who are not admins to be able to create custom links in a group. They cannot because the route entity.group_content_menu.add_link requires the group permission create group_content_menu:default_group_menu content, which does not exist.

Proposed resolution

Add full CRUD permissions, or change the check on this route.