### 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 INCREASE_SHARD_LIMIT_ACTION_GUIDE = "https://ela.st/index-total-shards";
    public static final Diagnosis.Definition ACTION_INCREASE_SHARD_LIMIT_INDEX_SETTING = new Diagnosis.Definition(
        NAME,
        "increase_shard_limit_index_setting",
        "Elasticsearch isn't allowed to allocate some shards from these indices to any data nodes because each node has reached the index "
            + "shard limit. ",
        "Increase the values for the ["
            + INDEX_TOTAL_SHARDS_PER_NODE_SETTING.getKey()
            + "] index setting on each index or add more nodes to the target tiers.",
        INCREASE_SHARD_LIMIT_ACTION_GUIDE
    );
    public static final Map<String, Diagnosis.Definition> ACTION_INCREASE_SHARD_LIMIT_INDEX_SETTING_LOOKUP = DataTier.ALL_DATA_TIERS
        .stream()
        .collect(
            Collectors.toUnmodifiableMap(
                tier -> tier,
                tier -> new Diagnosis.Definition(
                    NAME,
                    "increase_shard_limit_index_setting:tier:" + tier,
                    "Elasticsearch isn't allowed to allocate some shards from these indices because each node in the ["
                        + tier
                        + "] tier has reached the index shard limit. ",
                    "Increase the values for the ["
                        + INDEX_TOTAL_SHARDS_PER_NODE_SETTING.getKey()
                        + "] index setting on each index or add more nodes to the target tiers.",
                    INCREASE_SHARD_LIMIT_ACTION_GUIDE
                )
            )
        );