### 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
List.of()
        );
        var service = createShardsAvailabilityIndicatorService(clusterState);
        HealthIndicatorResult result = service.calculate(true, HealthInfo.EMPTY_HEALTH_INFO);
        assertEquals(RED, result.status());
        assertEquals("This cluster has 1 unavailable primary shard, 2 unavailable replica shards.", result.symptom());
        assertEquals(2, result.impacts().size());
        assertEquals(
            result.impacts().get(0),
            new HealthIndicatorImpact(
                NAME,
                ShardsAvailabilityHealthIndicatorService.PRIMARY_UNASSIGNED_IMPACT_ID,
                1,
                "Cannot add data to 1 index [red-index]. Searches might return incomplete results.",
                List.of(ImpactArea.INGEST, ImpactArea.SEARCH)
            )
        );
        
        assertThat(
            result.impacts().get(1),
            equalTo(
                new HealthIndicatorImpact(
                    NAME,
                    ShardsAvailabilityHealthIndicatorService.REPLICA_UNASSIGNED_IMPACT_ID,
                    2,
                    "Searches might be slower than usual. Fewer redundant copies of the data exist on 2 indices [yellow-index-2, "
                        + "yellow-index-1].",
                    List.of(ImpactArea.SEARCH)
                )
            )