### 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/node/Node.java
import static org.elasticsearch.core.Types.forciblyCast;
/**
 * A node represent a node within a cluster ({@code cluster.name}). The {@link #client()} can be used
 * in order to use a {@link Client} to perform actions/operations against the cluster.
 */
public class Node implements Closeable {
    public static final Setting<Boolean> WRITE_PORTS_FILE_SETTING = Setting.boolSetting("node.portsfile", false, Property.NodeScope);
    public static final Setting<String> NODE_NAME_SETTING = Setting.simpleString("node.name", Property.NodeScope);
    public static final Setting<String> NODE_EXTERNAL_ID_SETTING = Setting.simpleString(
        "node.external_id",
        NODE_NAME_SETTING,
        Property.NodeScope
    );
    public static final Setting.AffixSetting<String> NODE_ATTRIBUTES = Setting.prefixKeySetting(
        "node.attr.",
        (key) -> new Setting<>(key, "", (value) -> {
            if (value.length() > 0
                && (Character.isWhitespace(value.charAt(0)) || Character.isWhitespace(value.charAt(value.length() - 1)))) {
                throw new IllegalArgumentException(key + " cannot have leading or trailing whitespace [" + value + "]");
            }
            if (value.length() > 0 && "node.attr.server_name".equals(key)) {
                try {
                    new SNIHostName(value);
                } catch (IllegalArgumentException e) {
                    throw new IllegalArgumentException("invalid node.attr.server_name [" + value + "]", e);
                }
            }
            return value;
        }, Property.NodeScope)
    );