discussions: fix configurable BBA URL in ticket description
    
    The URL was supposed to be configurable, but wasn't, because the URL was baked
    into the ticket template during initial startup and the BLOCKERBUGS_URL config
    option no longer affected it. This fixes it.
    
    Related: https://pagure.io/fedora-qa/blockerbugs/issue/192
    Merges: https://pagure.io/fedora-qa/blockerbugs/pull-request/212