### 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 testShouldBeRedWhenThereAreUnassignedPrimariesAndAssignedReplicas() {
        var clusterState = createClusterStateWith(
            List.of(index("red-index", new ShardAllocation(randomNodeId(), UNAVAILABLE), new ShardAllocation(randomNodeId(), AVAILABLE))),
            List.of()
        );
        var service = createShardsAvailabilityIndicatorService(clusterState);
        assertThat(
            service.calculate(true, HealthInfo.EMPTY_HEALTH_INFO),
            equalTo(
                createExpectedResult(
                    RED,
                    "This cluster has 1 unavailable primary shard.",
                    Map.of("unassigned_primaries", 1, "started_replicas", 1),
                    List.of(
                        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)
                        )
                    ),
                    List.of(
                        new Diagnosis(ACTION_CHECK_ALLOCATION_EXPLAIN_API, List.of(new Diagnosis.Resource(INDEX, List.of("red-index"))))
                    )
                )
            )
        );