### 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
if (LOGGER.isTraceEnabled()) {
                LOGGER.trace(
                    "[{}]: Working with decisions: [{}]",
                    shardRouting.shardId(),
                    allocateDecision.getNodeDecisions()
                        .stream()
                        .map(
                            n -> n.getCanAllocateDecision()
                                .getDecisions()
                                .stream()
                                .map(d -> d.label() + ": " + d.type())
                                .collect(Collectors.toList())
                        )
                        .collect(Collectors.toList())
                );
            }
            List<NodeAllocationResult> nodeAllocationResults = allocateDecision.getNodeDecisions();
            return diagnoseAllocationResults(shardRouting, state, nodeAllocationResults);
        } else {
            return List.of();
        }
    }
    /**
     * Generates a list of diagnoses for an unassigned shard by inspecting a list of NodeAllocationResults for
     * well known problems.
     * @param shardRouting The unassigned shard.
     * @param state Current cluster state.
     * @param nodeAllocationResults A list of results for each node in the cluster from the allocation explain api
     * @return A list of diagnoses for the provided unassigned shard
     */