### 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
public static final String DIAGNOSE_SHARDS_ACTION_GUIDE = "https://ela.st/diagnose-shards";
    public static final Diagnosis.Definition ACTION_CHECK_ALLOCATION_EXPLAIN_API = new Diagnosis.Definition(
        NAME,
        "explain_allocations",
        "Elasticsearch isn't allowed to allocate some shards from these indices to any of the nodes in the cluster.",
        "Diagnose the issue by calling the allocation explain API for an index [GET _cluster/allocation/explain]. Choose a node to which "
            + "you expect a shard to be allocated, find this node in the node-by-node explanation, and address the reasons which prevent "
            + "Elasticsearch from allocating the shard.",
        DIAGNOSE_SHARDS_ACTION_GUIDE
    );
    public static final String FIX_DELAYED_SHARDS_GUIDE = "https://ela.st/fix-delayed-shard-allocation";
    public static final Diagnosis.Definition DIAGNOSIS_WAIT_FOR_OR_FIX_DELAYED_SHARDS = new Diagnosis.Definition(
        NAME,
        "delayed_shard_allocations",
        "Elasticsearch is not allocating some shards because they are marked for delayed allocation. Shards that have become "
            + "unavailable are usually marked for delayed allocation because it is more efficient to wait and see if the shards return "
            + "on their own than to recover the shard immediately.",
        "Elasticsearch will reallocate the shards when the delay has elapsed. No action is required by the user.",
        FIX_DELAYED_SHARDS_GUIDE
    );
    public static final String ENABLE_INDEX_ALLOCATION_GUIDE = "https://ela.st/fix-index-allocation";
    public static final Diagnosis.Definition ACTION_ENABLE_INDEX_ROUTING_ALLOCATION = new Diagnosis.Definition(
        NAME,
        "enable_index_allocations",
        "Elasticsearch isn't allowed to allocate some shards from these indices because allocation for those shards has been disabled at "
            + "the index level.",
        "Check that the ["
            + INDEX_ROUTING_ALLOCATION_ENABLE_SETTING.getKey()
            + "] index settings are set to ["
            + EnableAllocationDecider.Allocation.ALL.toString().toLowerCase(Locale.getDefault())