### 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<Diagnosis.Definition> definitions = service.diagnoseUnassignedShardRouting(shardRouting, ClusterState.EMPTY_STATE);
        assertThat(definitions, hasSize(1));
        assertThat(definitions, contains(ACTION_RESTORE_FROM_SNAPSHOT));
    }
    public void testDiagnoseUnknownAllocationDeciderIssue() {
        
        IndexMetadata indexMetadata = IndexMetadata.builder("red-index")
            .settings(Settings.builder().put(IndexMetadata.SETTING_VERSION_CREATED, Version.CURRENT).build())
            .numberOfShards(1)
            .numberOfReplicas(0)
            .build();
        
        var clusterState = createClusterStateWith(
            List.of(indexMetadata),
            List.of(index("red-index", new ShardAllocation(randomNodeId(), UNAVAILABLE, randomFrom(decidersNo(), nodeLeft())))),
            List.of(),
            List.of()
        );
        
        Map<ShardRoutingKey, ShardAllocationDecision> decisionMap = Map.of(
            new ShardRoutingKey("red-index", 0, true),
            new ShardAllocationDecision(
                AllocateUnassignedDecision.fromDecision(
                    Decision.NO,
                    null,
                    List.of(
                        new NodeAllocationResult(
                            new DiscoveryNode(randomNodeId(), buildNewFakeTransportAddress(), Version.CURRENT),
                            new Decision.Multi().add(Decision.single(Decision.Type.YES, EnableAllocationDecider.NAME, null))
                                .add(Decision.single(Decision.Type.YES, "data_tier", null))