### 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
DiscoveryNode newNode = createNode(Version.V_7_6_0, DiscoveryNodeRole.MASTER_ROLE, DiscoveryNodeRole.DATA_ROLE); 
                                                                                                                             
                                                                                                                             
            state = cluster.addNode(state, newNode);
            
            state = cluster.updateSettings(
                state,
                new UpdateSettingsRequest("index").settings(
                    Settings.builder().put(IndexMetadata.INDEX_ROUTING_EXCLUDE_GROUP_PREFIX + "._name", oldNode.getName()).build()
                )
            );
            while (state.routingTable().index("index").shard(0).allShardsStarted() == false) {
                logger.info(state);
                state = cluster.applyStartedShards(
                    state,
                    state.routingTable().index("index").shard(0).shardsWithState(ShardRoutingState.INITIALIZING)
                );
                state = cluster.reroute(state, new ClusterRerouteRequest());
            }
            
            assertThat(state.routingTable().index("index").shard(0).size(), equalTo(3));
            
            state = cluster.removeNodes(state, Collections.singletonList(oldNode));
            assertThat(state.routingTable().index("index").shard(0).size(), equalTo(2));
        } finally {
            terminate(threadPool);
        }
    }
}