Summary

Add CLI support for frr_exporter optional collectors (bgpl2vpn, pim, vrrp) and collector options (BGP peer labels, OSPF instances, detailed route counts) under service monitoring prometheus frr-exporter collectors.

Use case

frr_exporter only enables the bgp, ospf, bfd and route collectors by default. Users running EVPN (bgpl2vpn), multicast (pim) or VRRP cannot monitor those protocols because VyOS provides no CLI to enable the corresponding collectors. Collector options are also useful for operators, e.g. --collector.bgp.peer-descriptions / peer-groups / peer-hostnames add labels to per-peer metrics for identifying BGP sessions in dashboards, and --collector.bgp.peer-types allows aggregating session state by peer type (transit/peering/customer).

Additional information

All exposed flags exist in frr_exporter v1.5.0 as currently packaged by vyos-build. The new CLI follows the existing node-exporter collectors style (opt-in valueless nodes). The bgp6 collector stays unconditionally enabled as introduced by T7851, so existing configurations render an identical systemd unit and no migration is needed. Note the collector.bgp.* options are shared upstream by the bgp, bgp6 and bgpl2vpn collectors. Smoketest updated accordingly.