Oxidized can be configured via the web GUI in Global Settings → External → Oxidized Integration
To override the GUI and force the config (not editable via the GUI anymore) configure in config.php
#------------------------#
# Oxidized Configuration #
#------------------------#
$config['oxidized']['enabled'] = TRUE;
$config['oxidized']['url'] = 'http://oxidized.int.mydomain.net:8888';
$config['oxidized']['features']['versioning'] = true;