### 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
}
    private record ShardAllocation(String nodeId, ShardState state, Long unassignedTimeNanos, @Nullable UnassignedInfo unassignedInfo) {
        ShardAllocation(String nodeId, ShardState state) {
            this(nodeId, state, null, null);
        }
        ShardAllocation(String nodeId, ShardState state, Long unassignedTimeNanos) {
            this(nodeId, state, unassignedTimeNanos, null);
        }
        ShardAllocation(String nodeId, ShardState state, UnassignedInfo unassignedInfo) {
            this(nodeId, state, null, unassignedInfo);
        }
    }
    private record NodeShutdown(String nodeId, SingleNodeShutdownMetadata.Type type, Integer allocationDelaySeconds) {}
    private static String randomNodeId() {
        return UUID.randomUUID().toString();
    }
    private static UnassignedInfo noShardCopy() {
        return new UnassignedInfo(
            randomBoolean() ? UnassignedInfo.Reason.NODE_LEFT : UnassignedInfo.Reason.CLUSTER_RECOVERED,
            null,
            null,
            0,
            0,
            0,
            false,
            UnassignedInfo.AllocationStatus.NO_VALID_SHARD_COPY,
            Collections.emptySet(),
            null
        );
    }