### 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
}
    public OptionalInt getDesiredNumberOfReplicas(IndexMetadata indexMetadata, RoutingAllocation allocation) {
        assert enabled : "should only be called when enabled";
        int numMatchingDataNodes = 0;
        for (DiscoveryNode discoveryNode : allocation.nodes().getDataNodes().values()) {
            Decision decision = allocation.deciders().shouldAutoExpandToNode(indexMetadata, discoveryNode, allocation);
            if (decision.type() != Decision.Type.NO) {
                numMatchingDataNodes++;
            }
        }
        final int min = minReplicas();
        final int max = getMaxReplicas(numMatchingDataNodes);
        int numberOfReplicas = numMatchingDataNodes - 1;
        if (numberOfReplicas < min) {
            numberOfReplicas = min;
        } else if (numberOfReplicas > max) {
            numberOfReplicas = max;
        }
        if (numberOfReplicas >= min && numberOfReplicas <= max) {
            return OptionalInt.of(numberOfReplicas);
        }
        return OptionalInt.empty();
    }
    @Override
    public String toString() {
        return enabled ? minReplicas + "-" + maxReplicas : "false";
    }
    /**
     * Checks if there are replicas with the auto-expand feature that need to be adapted.
     * Returns a map of updates, which maps the indices to be updated to the desired number of replicas.