vault: use make_app_from_configfile() for gunicorn
vault: use make_app_from_configfile() for gunicorn

SoftwareHeritage/puppet-swh-profile,SoftwareHeritage/puppet-swh-site,SoftwareHeritage/puppet-swh-profile,SoftwareHeritage/puppet-swh-profile,SoftwareHeritage/puppet-swh-site,SoftwareHeritage/puppet-swh-site,SoftwareHeritage/puppet-swh-profile,SoftwareHeritage/puppet-swh-site,SoftwareHeritage/puppet-swh-profile,SoftwareHeritage/puppet-swh-site