### 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/cluster/routing/allocation/ShardsAvailabilityHealthIndicatorService.java
private boolean available = true; 
        private int unassigned = 0;
        private int unassigned_new = 0;
        private int unassigned_restarting = 0;
        private int initializing = 0;
        private int started = 0;
        private int relocating = 0;
        private final Set<String> indicesWithUnavailableShards = new HashSet<>();
        private final Map<Diagnosis.Definition, Set<String>> diagnosisDefinitions = new HashMap<>();
        public void increment(ShardRouting routing, ClusterState state, NodesShutdownMetadata shutdowns, boolean verbose) {
            boolean isNew = isUnassignedDueToNewInitialization(routing);
            boolean isRestarting = isUnassignedDueToTimelyRestart(routing, shutdowns);
            available &= routing.active() || isRestarting || isNew;
            if ((routing.active() || isRestarting || isNew) == false) {
                indicesWithUnavailableShards.add(routing.getIndexName());
            }
            switch (routing.state()) {
                case UNASSIGNED -> {
                    if (isNew) {
                        unassigned_new++;
                    } else if (isRestarting) {
                        unassigned_restarting++;
                    } else {
                        unassigned++;
                        if (verbose) {