[inventory] Add unhealthy zpools from each sled

[karencfv]

This is the second PR for #9412

This commit adds a list of unhealthy zpools to the sled agent inventory's health monitor. In a follow-up PR this information will be added to the DB

Successful unhealthy zpool retrieval:

$ zpool list -Hpo health,name
FAULTED fakepool1
FAULTED fakepool2
ONLINE  rpool

$ curl -H "api-version: 15.0.0"  http://[::1]:54963/inventory | jq
<...>
  "health_monitor": {
    "smf_services_in_maintenance": {
      "ok": {
        "services": [
          {
            "fmri": "svc:/site/fake-service2:default",
            "zone": "global"
          }
        ],
        "errors": [],
        "time_of_status": "2026-01-12T07:15:06.913644164Z"
      }
    },
    "unhealthy_zpools": {
      "ok": {
        "zpools": [
          "fakepool1",
          "fakepool2"
        ],
        "errors": [],
        "time_of_status": "2026-01-12T07:15:06.888312628Z"
      }
    }
  }

Response contains errors:

$ curl -H "api-version: 15.0.0"  http://[::1]:54963/inventory | jq
<...>
  "health_monitor": {
    "smf_services_in_maintenance": {
      "ok": {
        "services": [],
        "errors": [],
        "time_of_status": "2026-01-12T07:10:00.642206104Z"
      }
    },
    "unhealthy_zpools": {
      "ok": {
        "zpools": [],
        "errors": [
          "Failed to parse output: Unrecognized zpool 'health': fakepool1",
          "Failed to parse output: Unrecognized zpool 'health': fakepool2",
          "Failed to parse output: Unrecognized zpool 'health': rpool"
        ],
        "time_of_status": "2026-01-12T07:10:00.591985515Z"
      }
    }
  }

[jgallagher]

Does this need to be optional? If we have a result, it must have been collected at some time, right?

[karencfv]

This is meant for when this runs on non-illumos environements

https://github.com/oxidecomputer/omicron/pull/9615/files#diff-07cfb91c0643fac6671e8b81317c92cbe806ab07e2af6fdce16db75315245e32R446-R453

The idea is that there is no time of status because no command was ever run.

[karencfv]

Also there is a point in time where health monitor may not have run yet -> #9589 (comment)

[karencfv]

I went back and forth between just having a list of unhealthy zpools, or associating each zpool with it's state. In the end I went with listing the zpools only, but I'm not convinced. We'll be including the information of the health checks in the support bundle, and it'd be useful for them to be able to see what state each zpool is in. Thoughts? @davepacheco @jgallagher