### 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/test/java/org/elasticsearch/cluster/metadata/AutoExpandReplicasTests.java
/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0 and the Server Side Public License, v 1; you may not use this file except
 * in compliance with, at your election, the Elastic License 2.0 or the Server
 * Side Public License, v 1.
 */
package org.elasticsearch.cluster.metadata;
import org.elasticsearch.Version;
import org.elasticsearch.action.admin.cluster.reroute.ClusterRerouteRequest;
import org.elasticsearch.action.admin.indices.create.CreateIndexRequest;
import org.elasticsearch.action.admin.indices.settings.put.UpdateSettingsRequest;