
**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)

{
    for (const auto & shard_info : shards_info)
    {
        if (!shard_info.isLocal() && !shard_info.hasRemoteConnections())
            throw Exception("Found shard without any specified connection",
                ErrorCodes::SHARD_HAS_NO_CONNECTIONS);
    }
    for (const auto & shard_info : shards_info)
    {
        if (shard_info.isLocal())
            ++local_shard_count;
        else
            ++remote_shard_count;
    }
    for (auto & shard_info : shards_info)
    {
        if (!shard_info.isLocal())
        {
            any_remote_shard_info = &shard_info;
            break;
        }
    }
}
std::unique_ptr<Cluster> Cluster::getClusterWithReplicasAsShards(const Settings & settings) const