status json: list the unhealthy_servers under cluster.data.team_trackers

In the `team_trackers` sections of `status json`, we output the number of unhealthy servers. We should also be listing them explicitly either by id or ip:port to enable easier debugging:

```
"data": {
"team_trackers":[
{
"primary":true,
"in_flight_bytes":0,
"unhealthy_servers":0,
"state":{
"healthy":true,
"min_replicas_remaining":0,
"name":{ // when not limiting
"$enum":[
"initializing",
"missing_data",
"healing",
"optimizing_team_collections",
"healthy_populating_region",
"healthy_repartitioning",
"healthy_removing_server",
"healthy_rebalancing",
"healthy"
]
},
"description":""
}
}
],
}
```

Start by locating the C++ code that generates the cluster status JSON and the team_trackers section, then inspect how unhealthy_servers is currently counted. Done means the status output lists each unhealthy server by id or ip:port in addition to the count; the payload names no files or tests.

Written by the indexing model from the issue text.