### Elasticsearch Version

All

### Installed Plugins

N/A

### Java Version

_bundled_

### OS Version

N/A

### Problem Description

Today if an index has an `index.auto_expand_replicas` setting which cannot be realised in the cluster then the number of replicas is left unchanged by `AllocationService#adaptAutoExpandReplicas()`. Instead, I think we should change the number of replicas to the closest value within the permitted range.

For instance: if a cluster has a single data node which is marked as shutting down for restart then auto-expand replicas considers this cluster to have zero data nodes, and hence requires -1 replicas. If an index is created with `index.auto_expand_replicas: "0-1"` then it will not be adjusted to have zero replicas, even though this would be better than leaving it at the default value of 1 replica, and will ultimately be the correct setting.

### Steps to Reproduce

1. Create a cluster with one data node.
2. Put a `RESTART` shutdown marker on the data node.
3. Create an index with `index.auto_expand_replicas: "0-1"`
4. Observe that this results in an unassigned replica.

### Logs (if relevant)

_No response_
server/src/main/java/org/elasticsearch/cluster/metadata/AutoExpandReplicas.java
* The map has the desired number of replicas as key and the indices to update as value, as this allows the result
     * of this method to be directly applied to RoutingTable.Builder#updateNumberOfReplicas.
     */
    public static Map<Integer, List<String>> getAutoExpandReplicaChanges(
        Metadata metadata,
        Supplier<RoutingAllocation> allocationSupplier
    ) {
        Map<Integer, List<String>> nrReplicasChanged = new HashMap<>();
        
        RoutingAllocation allocation = null;
        for (final IndexMetadata indexMetadata : metadata) {
            if (indexMetadata.getState() == IndexMetadata.State.OPEN || isIndexVerifiedBeforeClosed(indexMetadata)) {
                AutoExpandReplicas autoExpandReplicas = indexMetadata.getAutoExpandReplicas();
                if (autoExpandReplicas.enabled() == false) {
                    continue;
                }
                if (allocation == null) {
                    allocation = allocationSupplier.get();
                }
                autoExpandReplicas.getDesiredNumberOfReplicas(indexMetadata, allocation).ifPresent(numberOfReplicas -> {
                    if (numberOfReplicas != indexMetadata.getNumberOfReplicas()) {
                        nrReplicasChanged.computeIfAbsent(numberOfReplicas, ArrayList::new).add(indexMetadata.getIndex().getName());
                    }
                });
            }
        }
        return nrReplicasChanged;
    }
}