### 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/main/java/org/elasticsearch/cluster/routing/allocation/ShardsAvailabilityHealthIndicatorService.java
.stream()
                    .filter(dataTierRolesAvailable::contains)
                    .findFirst()
                    .orElse(null);
                
                diagnosisDefs.addAll(
                    checkDataTierAtShardLimit(indexMetadata, clusterState, dataTierAllocationResults, dataTierNodes, preferredTier)
                );
                diagnosisDefs.addAll(checkDataTierShouldMigrate(indexMetadata, dataTierAllocationResults, preferredTier, dataTierNodes));
                checkNotEnoughNodesInDataTier(dataTierAllocationResults, preferredTier).ifPresent(diagnosisDefs::add);
            }
        }
        return diagnosisDefs;
    }
    private List<Diagnosis.Definition> checkDataTierAtShardLimit(
        IndexMetadata indexMetadata,
        ClusterState clusterState,
        List<NodeAllocationResult> dataTierAllocationResults,
        Set<DiscoveryNode> dataTierNodes,
        @Nullable String preferredTier
    ) {
        
        if (dataTierAllocationResults.stream().allMatch(hasDeciderResult(ShardsLimitAllocationDecider.NAME, Decision.Type.NO))) {
            List<Diagnosis.Definition> diagnosisDefs = new ArrayList<>();
            
            List<RoutingNode> dataTierRoutingNodes = clusterState.getRoutingNodes()
                .stream()
                .filter(routingNode -> dataTierNodes.contains(routingNode.node()))
                .toList();