### 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
);
    }
    public void testSortByIndexPriority() {
        var lowPriority = randomIntBetween(1, 5);
        var highPriority = randomIntBetween(6, 20);
        List<IndexMetadata> indexMetadataList = createIndexMetadataForIndexNameToPriorityMap(
            Map.of("index-3", lowPriority, "index-1", lowPriority, "index-2", highPriority)
        );
        var clusterState = createClusterStateWith(
            indexMetadataList,
            List.of(
                index("index-3", new ShardAllocation(randomNodeId(), AVAILABLE), new ShardAllocation(randomNodeId(), UNAVAILABLE)),
                index("index-1", new ShardAllocation(randomNodeId(), AVAILABLE), new ShardAllocation(randomNodeId(), UNAVAILABLE)),
                index("index-2", new ShardAllocation(randomNodeId(), AVAILABLE), new ShardAllocation(randomNodeId(), UNAVAILABLE))
            ),
            List.of(),
            List.of()
        );
        var service = createShardsAvailabilityIndicatorService(clusterState);
        HealthIndicatorResult result = service.calculate(true, HealthInfo.EMPTY_HEALTH_INFO);
        
        assertThat(
            result.impacts().get(0),
            equalTo(
                new HealthIndicatorImpact(
                    NAME,
                    ShardsAvailabilityHealthIndicatorService.REPLICA_UNASSIGNED_IMPACT_ID,
                    2,
                    "Searches might be slower than usual. Fewer redundant copies of the data exist on 3 indices [index-2, "
                        + "index-1, index-3].",