### 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
it -> it.nodeId,
                        it -> SingleNodeShutdownMetadata.builder()
                            .setNodeId(it.nodeId)
                            .setType(it.type)
                            .setReason("test")
                            .setNodeSeen(true)
                            .setStartedAtMillis(System.currentTimeMillis())
                            .setAllocationDelay(it.allocationDelaySeconds != null ? timeValueSeconds(it.allocationDelaySeconds) : null)
                            .build()
                    )
                )
        );
        Metadata.Builder metadataBuilder = Metadata.builder();
        Map<String, IndexMetadata> indexMetadataMap = new HashMap<>();
        for (IndexMetadata indexMetadata : indexMetadataList) {
            indexMetadataMap.put(indexMetadata.getIndex().getName(), indexMetadata);
        }
        metadataBuilder.indices(indexMetadataMap);
        metadataBuilder.putCustom(NodesShutdownMetadata.TYPE, nodesShutdownMetadata);
        DiscoveryNodes.Builder discoveryNodesBuilder = DiscoveryNodes.builder();
        nodes.forEach(discoveryNodesBuilder::add);
        return ClusterState.builder(new ClusterName("test-cluster"))
            .routingTable(routingTableBuilder.build())
            .nodes(discoveryNodesBuilder)
            .metadata(metadataBuilder.build())
            .build();
    }
    private static Map<String, Object> addDefaults(Map<String, Object> override) {
        return Map.of(
            "unassigned_primaries",