Create PDC release in addition to PDC product-version.
    
    This is part of the puzzle for https://pagure.io/fedora-infrastructure/issue/6729
    
    This creates the "release" in addition to the product version, so that tools
    like fedrepo-req can find out about the active product-version.  The
    product-version was previously created, but without an associated version it
    was counted as inactive.
    
    - I ran this and created
      https://pdc.fedoraproject.org/rest_api/v1/releases/fedora-28/
    - which makes this product-version active
      https://pdc.fedoraproject.org/rest_api/v1/product-versions/fedora-28/
    
    Signed-off-by: Ralph Bean <rbean@redhat.com>