### 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/health/Diagnosis.java
return type == resource.type && Objects.equals(values, resource.values) && Objects.equals(nodes, resource.nodes);
        }
        @Override
        public int hashCode() {
            return Objects.hash(type, values, nodes);
        }
        public Type getType() {
            return type;
        }
        @Nullable
        public Collection<String> getValues() {
            return values;
        }
        @Nullable
        public Collection<DiscoveryNode> getNodes() {
            return nodes;
        }
    }
    /**
     * Details a diagnosis - cause and a potential action that a user could take to clear an issue identified by a {@link HealthService}.
     *
     * @param indicatorName The name of the health indicator service that will generate this diagnosis
     * @param id An identifier unique to this diagnosis across the health indicator that generates it
     * @param cause A description of the cause of the problem
     * @param action A description of the action to be taken to remedy the problem
     * @param helpURL Optional evergreen url to a help document
     */
    public record Definition(String indicatorName, String id, String cause, String action, String helpURL) {
        public String getUniqueId() {
            return HEALTH_API_ID_PREFIX + indicatorName + ":diagnosis:" + id;