### 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
public void testShouldBeGreenWhenThereAreNoReplicasExpected() {
        var clusterState = createClusterStateWith(
            List.of(index("primaries-only-index", new ShardAllocation(randomNodeId(), AVAILABLE))),
            List.of(new NodeShutdown("node-0", RESTART, 60))
        );
        var service = createShardsAvailabilityIndicatorService(clusterState);
        assertThat(
            service.calculate(true, HealthInfo.EMPTY_HEALTH_INFO),
            equalTo(
                createExpectedResult(
                    GREEN,
                    "This cluster has all shards available.",
                    Map.of("started_primaries", 1),
                    Collections.emptyList(),
                    Collections.emptyList()
                )
            )
        );
    }
    public void testShouldBeYellowWhenRestartingReplicasReachedAllocationDelay() {
        var clusterState = createClusterStateWith(
            List.of(
                index(
                    "restarting-index",
                    new ShardAllocation(randomNodeId(), AVAILABLE),
                    new ShardAllocation("node-0", RESTARTING, System.nanoTime() - timeValueSeconds(between(60, 180)).nanos())
                )
            ),
            List.of(new NodeShutdown("node-0", RESTART, 60))
        );