### 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
state,
                    state.routingTable().index("index").shard(0).shardsWithState(ShardRoutingState.INITIALIZING)
                );
                state = cluster.reroute(state, new ClusterRerouteRequest());
            }
            IndexShardRoutingTable preTable = state.routingTable().index("index").shard(0);
            final Set<String> unchangedNodeIds;
            final IndexShardRoutingTable postTable;
            if (randomBoolean()) {
                
                List<DiscoveryNode> nodesToRemove = randomSubsetOf(2, dataNodes);
                unchangedNodeIds = dataNodes.stream()
                    .filter(n -> nodesToRemove.contains(n) == false)
                    .map(DiscoveryNode::getId)
                    .collect(Collectors.toSet());
                state = cluster.removeNodes(state, nodesToRemove);
                postTable = state.routingTable().index("index").shard(0);
                assertTrue("not all shards started in " + state.toString(), postTable.allShardsStarted());
                assertThat(postTable.toString(), postTable.getAllAllocationIds(), everyItem(is(in(preTable.getAllAllocationIds()))));
            } else {
                
                state = ClusterState.builder(state).nodes(DiscoveryNodes.builder(state.nodes()).masterNodeId(null).build()).build();
                List<DiscoveryNode> conflictingNodes = randomSubsetOf(2, dataNodes);
                unchangedNodeIds = dataNodes.stream()
                    .filter(n -> conflictingNodes.contains(n) == false)
                    .map(DiscoveryNode::getId)
                    .collect(Collectors.toSet());
                List<DiscoveryNode> nodesToAdd = conflictingNodes.stream()
                    .map(
                        n -> new DiscoveryNode(