### 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
ClusterModule.getNamedXWriteables().stream(),
                    SystemIndexMigrationExecutor.getNamedXContentParsers().stream(),
                    HealthNodeTaskExecutor.getNamedXContentParsers().stream()
                ).flatMap(Function.identity()).collect(toList())
            );
            final List<SystemIndices.Feature> features = pluginsService.filterPlugins(SystemIndexPlugin.class).stream().map(plugin -> {
                SystemIndices.validateFeatureName(plugin.getFeatureName(), plugin.getClass().getCanonicalName());
                return SystemIndices.Feature.fromSystemIndexPlugin(plugin, settings);
            }).toList();
            final SystemIndices systemIndices = new SystemIndices(features);
            final ExecutorSelector executorSelector = systemIndices.getExecutorSelector();
            ModulesBuilder modules = new ModulesBuilder();
            final MonitorService monitorService = new MonitorService(settings, nodeEnvironment, threadPool);
            final FsHealthService fsHealthService = new FsHealthService(
                settings,
                clusterService.getClusterSettings(),
                threadPool,
                nodeEnvironment
            );
            final SetOnce<RerouteService> rerouteServiceReference = new SetOnce<>();
            final InternalSnapshotsInfoService snapshotsInfoService = new InternalSnapshotsInfoService(
                settings,
                clusterService,
                repositoriesServiceReference::get,
                rerouteServiceReference::get
            );
            final WriteLoadForecaster writeLoadForecaster = getWriteLoadForecaster(
                threadPool,
                settings,
                clusterService.getClusterSettings()