### 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
+ "].",
        ENABLE_INDEX_ALLOCATION_GUIDE
    );
    public static final String ENABLE_CLUSTER_ALLOCATION_ACTION_GUIDE = "https://ela.st/fix-cluster-allocation";
    public static final Diagnosis.Definition ACTION_ENABLE_CLUSTER_ROUTING_ALLOCATION = new Diagnosis.Definition(
        NAME,
        "enable_cluster_allocations",
        "Elasticsearch isn't allowed to allocate some shards from these indices because allocation for those shards has been disabled at "
            + "the cluster level.",
        "Check that the ["
            + EnableAllocationDecider.CLUSTER_ROUTING_ALLOCATION_ENABLE_SETTING.getKey()
            + "] cluster setting is set to ["
            + EnableAllocationDecider.Allocation.ALL.toString().toLowerCase(Locale.getDefault())
            + "].",
        ENABLE_CLUSTER_ALLOCATION_ACTION_GUIDE
    );
    public static final String ENABLE_TIER_ACTION_GUIDE = "https://ela.st/enable-tier";
    public static final Map<String, Diagnosis.Definition> ACTION_ENABLE_TIERS_LOOKUP = DataTier.ALL_DATA_TIERS.stream()
        .collect(
            Collectors.toUnmodifiableMap(
                tier -> tier,
                tier -> new Diagnosis.Definition(
                    NAME,
                    "enable_data_tiers:tier:" + tier,
                    "Elasticsearch isn't allowed to allocate some shards from these indices because the indices expect to be allocated to "
                        + "data tier nodes, but there were not any nodes with the expected tiers found in the cluster.",
                    "Add nodes with the [" + tier + "] role to the cluster.",
                    ENABLE_TIER_ACTION_GUIDE
                )
            )