
**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)

"server", replica.compression, replica.secure, replica.priority);
            all_replicas.emplace_back(replica_pool);
            if (replica.is_local && !treat_local_as_remote)
                shard_local_addresses.push_back(replica);
        }
        ConnectionPoolWithFailoverPtr shard_pool = std::make_shared<ConnectionPoolWithFailover>(
                all_replicas, settings.load_balancing,
                settings.distributed_replica_error_half_life.totalSeconds(), settings.distributed_replica_error_cap);
        slot_to_shard.insert(std::end(slot_to_shard), default_weight, shards_info.size());
        shards_info.push_back({
            {}, 
            current_shard_num,
            default_weight,
            std::move(shard_local_addresses),
            std::move(shard_pool),
            std::move(all_replicas),
            false 
        });
        ++current_shard_num;
    }
    initMisc();
}
Poco::Timespan Cluster::saturate(const Poco::Timespan & v, const Poco::Timespan & limit)
{
    if (limit.totalMicroseconds() == 0)
        return v;
    else
        return (v > limit) ? limit : v;
}
void Cluster::initMisc()