
**Bug description**
Unlike `cluster()`, `clusterAllReplicas()` does not implement `_shard_num`. 

I would expect
```
SELECT _shard_num
FROM clusterAllReplicas(prod, system.one)
ORDER BY _shard_num ASC
FORMAT PrettyCompactMonoBlock

┌─_shard_num─┐
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
│          0 │
└────────────┘
```
to have an output more useful like
```
SELECT _shard_num
FROM cluster(prod, system.one)
ORDER BY _shard_num ASC
FORMAT PrettyCompactMonoBlock

┌─_shard_num─┐
│          1 │
│          2 │
│          3 │
│          4 │
│          5 │
│          6 │
│          7 │
│          8 │
│          9 │
│         10 │
│         11 │
│         12 │
│         13 │
│         14 │
│         15 │
└────────────┘
```

**Releases where this has been tested**

* v20.3.12.112-stable

**References**

[cluster, clusterAllReplicas documentation](https://clickhouse.tech/docs/en/sql-reference/table-functions/cluster/)

[_shard_num documentation](https://clickhouse.tech/docs/en/engines/table-engines/special/distributed/#virtual-columns)

old_config->keys(config_prefix, old_config_keys);
        std::sort(old_config_keys.begin(), old_config_keys.end());
        std::set_difference(
            old_config_keys.begin(), old_config_keys.end(), new_config_keys.begin(), new_config_keys.end(), std::back_inserter(deleted_keys));
    }
    std::lock_guard lock(mutex);
    
    if (old_config)
    {
        for (const auto & key : deleted_keys)
            impl.erase(key);
    }
    else
        impl.clear();
    for (const auto & key : new_config_keys)
    {
        if (key.find('.') != String::npos)
            throw Exception("Cluster names with dots are not supported: '" + key + "'", ErrorCodes::SYNTAX_ERROR);
        
        if (!old_config || !isSameConfiguration(new_config, *old_config, config_prefix + "." + key))
            impl[key] = std::make_shared<Cluster>(new_config, settings, config_prefix, key);
    }
}
Clusters::Impl Clusters::getContainer() const
{
    std::lock_guard lock(mutex);
    
    return impl;
}
Cluster::Cluster(const Poco::Util::AbstractConfiguration & config,