Add a new not-really-a-Next-button needle for gnome-initial-setup
    
    In g-i-s 3.37.91, the first screen has a 'Start Setup' button
    rather than a 'Next' button. Easiest thing for us to do here is
    just to add a new needle which has the 'next_button' tag even
    though it's clearly not a 'Next' button, because then the code
    still works :) So do that, but give the file a suggestive name
    and explain the situation in a code comment.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>