### 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/test/java/org/elasticsearch/cluster/routing/allocation/ShardsAvailabilityHealthIndicatorServiceTests.java
override.getOrDefault("unassigned_primaries", 0),
            "initializing_primaries",
            override.getOrDefault("initializing_primaries", 0),
            "creating_primaries",
            override.getOrDefault("creating_primaries", 0),
            "restarting_primaries",
            override.getOrDefault("restarting_primaries", 0),
            "started_primaries",
            override.getOrDefault("started_primaries", 0),
            "unassigned_replicas",
            override.getOrDefault("unassigned_replicas", 0),
            "initializing_replicas",
            override.getOrDefault("initializing_replicas", 0),
            "restarting_replicas",
            override.getOrDefault("restarting_replicas", 0),
            "started_replicas",
            override.getOrDefault("started_replicas", 0)
        );
    }
    private static IndexRoutingTable index(String name, ShardAllocation primaryState, ShardAllocation... replicaStates) {
        return index(
            IndexMetadata.builder(name)
                .settings(Settings.builder().put(IndexMetadata.SETTING_VERSION_CREATED, Version.CURRENT).build())
                .numberOfShards(1)
                .numberOfReplicas(replicaStates.length)
                .build(),
            primaryState,
            replicaStates
        );
    }