### 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
}
    }
    /**
     * The {@link PluginsService} used to build this node's components.
     */
    protected PluginsService getPluginsService() {
        return pluginsService;
    }
    /**
     * Plugins can provide additional settings for the node, but two plugins
     * cannot provide the same setting.
     * @param pluginMap A map of plugin names to plugin instances
     * @param originalSettings The node's original settings, which silently override any setting provided by the plugins.
     * @return A {@link Settings} with the merged node and plugin settings
     * @throws IllegalArgumentException if two plugins provide the same additional setting key
     */
    static Settings mergePluginSettings(Map<String, Plugin> pluginMap, Settings originalSettings) {
        Map<String, String> foundSettings = new HashMap<>();
        final Settings.Builder builder = Settings.builder();
        for (Map.Entry<String, Plugin> entry : pluginMap.entrySet()) {
            Settings settings = entry.getValue().additionalSettings();
            for (String setting : settings.keySet()) {
                String oldPlugin = foundSettings.put(setting, entry.getKey());
                if (oldPlugin != null) {
                    throw new IllegalArgumentException(
                        "Cannot have additional setting ["
                            + setting
                            + "] "
                            + "in plugin ["
                            + entry.getKey()