### 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
* @param indexMetadata from the index shard being diagnosed
     * @param nodeAllocationResults allocation decision results for all nodes in the cluster.
     * @return A list of diagnoses for the provided unassigned shard
     */
    List<Diagnosis.Definition> checkIsAllocationDisabled(IndexMetadata indexMetadata, List<NodeAllocationResult> nodeAllocationResults) {
        List<Diagnosis.Definition> diagnosisDefs = new ArrayList<>();
        if (nodeAllocationResults.stream().allMatch(hasDeciderResult(EnableAllocationDecider.NAME, Decision.Type.NO))) {
            
            Settings indexSettings = indexMetadata.getSettings();
            EnableAllocationDecider.Allocation indexLevelAllocation = INDEX_ROUTING_ALLOCATION_ENABLE_SETTING.get(indexSettings);
            ClusterSettings clusterSettings = clusterService.getClusterSettings();
            EnableAllocationDecider.Allocation clusterLevelAllocation = clusterSettings.get(
                EnableAllocationDecider.CLUSTER_ROUTING_ALLOCATION_ENABLE_SETTING
            );
            if (EnableAllocationDecider.Allocation.ALL != indexLevelAllocation) {
                
                diagnosisDefs.add(ACTION_ENABLE_INDEX_ROUTING_ALLOCATION);
            }
            if (EnableAllocationDecider.Allocation.ALL != clusterLevelAllocation) {
                
                diagnosisDefs.add(ACTION_ENABLE_CLUSTER_ROUTING_ALLOCATION);
            }
        }
        return diagnosisDefs;
    }
    /**
     * Generates a list of diagnoses for common problems that keep a shard from allocating to nodes in a data tier.
     * @param indexMetadata Index metadata for the shard being diagnosed.
     * @param nodeAllocationResults allocation decision results for all nodes in the cluster.
     * @param clusterState the current cluster state.