### 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);
        {
            
            assertThat(
                service.calculate(true, 2, HealthInfo.EMPTY_HEALTH_INFO),
                equalTo(
                    createExpectedResult(
                        RED,
                        "This cluster has 5 unavailable primary shards.",
                        Map.of("unassigned_primaries", 5, "started_replicas", 5),
                        List.of(
                            new HealthIndicatorImpact(
                                NAME,
                                ShardsAvailabilityHealthIndicatorService.PRIMARY_UNASSIGNED_IMPACT_ID,
                                1,
                                "Cannot add data to 5 indices [red-index1, red-index2, red-index3, red-index4, red-index5]. 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-index1", "red-index2")))
                            )
                        )
                    )