Add the pdc_import_compose toddler
    
    This toddler reacts to messages coming from pungi or playtime and inserts
    into PDC either the compose that was just done (when the notification
    comes from pungi) or finds in koji all the old composes and inserts them
    all (when the notification is coming from playtime).
    
    This toddler is the equivalent of the following handler in pdc-updater:
    https://github.com/fedora-infra/pdc-updater/blob/develop/pdcupdater/handlers/compose.py
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>