Add SNMP Extend Support for BIRD2

I'd like to request support for monitoring BIRD2 via SNMP in Observium. Currently, LibreNMS supports this through the SNMP extend mechanism, allowing BIRD2 metrics to be collected and visualized. This would allow for more complete visibility alongside the existing BGP monitoring.

Here is the relevant LibreNMS documentation and implementation for reference:

Docs: https://docs.librenms.org/Extensions/Applications/BIRD2/

Code: https://github.com/librenms/librenms/blob/master/includes/polling/applications/bird2.inc.php