`cadvisor` should be configurable to look for rootfs elsewhere

[james-callahan]

Request

Currently the cadvisor component looks in the current root / for all the information it wants.

I believe we need to figure out how to get a true plumbed through to inHostNamespace in https://github.com/google/cadvisor/blob/2129e1c4fae8567551d1ac252c7a1dec27617e21/container/containerd/factory.go#L80C3-L80C18

Slack link: https://grafana.slack.com/archives/C01050C3D8F/p1699607777165129

Use case

I wish to monitor my talos system containerd instance (see https://www.talos.dev/v1.5/learn-more/components/#containerd)

Trying:

prometheus.exporter.cadvisor "system" {
  containerd_host      = "/run/containerd/containerd.sock"
  containerd_namespace = "system"
}

prometheus.scrape "system_cadvisor" {
  targets    = prometheus.exporter.cadvisor.system.targets
  forward_to = [prometheus.relabel.system_cadvisor.receiver]
}

prometheus.relabel "system_cadvisor" {
  rule {
    target_label = "job"
    replacement  = "integrations/cadvisor/system"
  }
  forward_to = [prometheus.relabel.cadvisor.receiver]
}

Did scrape my containers, but didn't fill in many fields in including e.g. id. I believe these need various mount points such as /sys to work.

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