### 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/test/java/org/elasticsearch/cluster/routing/allocation/ShardsAvailabilityHealthIndicatorServiceTests.java
Map<String, Object> details,
        List<HealthIndicatorImpact> impacts,
        List<Diagnosis> diagnosisList
    ) {
        return new HealthIndicatorResult(
            NAME,
            status,
            symptom,
            new SimpleHealthIndicatorDetails(addDefaults(details)),
            impacts,
            diagnosisList
        );
    }
    private HealthIndicatorResult createExpectedTruncatedResult(HealthStatus status, String symptom, List<HealthIndicatorImpact> impacts) {
        return new HealthIndicatorResult(NAME, status, symptom, HealthIndicatorDetails.EMPTY, impacts, Collections.emptyList());
    }
    private static ClusterState createClusterStateWith(List<IndexRoutingTable> indexRoutes, List<NodeShutdown> nodeShutdowns) {
        List<IndexMetadata> indices = indexRoutes.stream()
            .map(
                table -> IndexMetadata.builder(table.getIndex().getName())
                    .settings(Settings.builder().put(IndexMetadata.SETTING_VERSION_CREATED, Version.CURRENT).build())
                    .numberOfShards(1)
                    .numberOfReplicas(table.size() - 1)
                    .build()
            )
            .collect(Collectors.toList());
        return createClusterStateWith(indices, indexRoutes, nodeShutdowns, List.of());
    }
    private static List<IndexMetadata> createIndexMetadataForIndexNameToPriorityMap(Map<String, Integer> indexNameToPriorityMap) {
        List<IndexMetadata> indexMetadataList = new ArrayList<>();