The `scrape_collectd_extra_targets` variable can be used to specify a
list of additional targets to scrape, in addition to the hosts in the
*collectd-prometheus* group. This will allow us to scrape hosts that
are not managed by the configuration policy, but still expose Prometheus
metrics via collectd.
The *scrape-collectd* role generates the
`/etc/prometheus/scrape-collectd.yml` file. This file can be read by
Prometheus/Victoria Metrics/vmagent to identify the hosts running
*collectd* with the *write_prometheus* plugin, using the
`files_sd_configs` scrape configuration option.
All hosts in the *collectd-prometheus* group are listed as scrape
targets.
