### Description

Elasticsearch defines the concept of a [feature](https://www.elastic.co/guide/en/elasticsearch/reference/current/get-features-api.html) for the purpose of better managing them when snapshotting/restoring them via the [feature_states field](https://www.elastic.co/guide/en/elasticsearch/reference/current/create-snapshot-api.html#create-snapshot-api-feature-states)

The `shards_availability` health indicator currently diagnoses the condition of indices needing to be [restored from a snapshot](https://github.com/elastic/elasticsearch/blob/main/server/src/main/java/org/elasticsearch/cluster/routing/allocation/ShardsAvailabilityHealthIndicatorService.java#L138) and recommends a [troubleshooting guide](http://ela.st/restore-snapshot)

However, since `8.x` the restore API **must** use `feature_states` instead of specifying systems indices or system data streams as part of the `indices` field.

This proposes the `affected_resources` for the `restore_from_snapshot` diagnosis return the indices that are not part of a `feature` under the `INDICES` type, and a new type `FEATURES`.
e.g. instead of current behaviour
```
"affected_resources": {
  "indices": [
    ".geoip_databases",
    "test_index"
    ]
}
```
we could return:
```
"affected_resources": {
  "indices": [
    "test_index"
   ], 
  "features": [
     "geoip"
  ]
}
```



server/src/main/java/org/elasticsearch/cluster/routing/allocation/ShardsAvailabilityHealthIndicatorService.java
});
                if (diagnosisToAffectedIndices.isEmpty()) {
                    return List.of();
                } else {
                    return diagnosisToAffectedIndices.entrySet()
                        .stream()
                        .map(
                            e -> new Diagnosis(
                                e.getKey(),
                                List.of(
                                    new Diagnosis.Resource(
                                        INDEX,
                                        e.getValue()
                                            .stream()
                                            .sorted(indicesComparatorByPriorityAndName(clusterMetadata))
                                            .limit(Math.min(e.getValue().size(), maxAffectedResourcesCount))
                                            .collect(Collectors.toList())
                                    )
                                )
                            )
                        )
                        .collect(Collectors.toList());
                }
            } else {
                return List.of();
            }
        }
    }
}