**Use case**

Currently, `system.replicas` table has `total_replicas` and `active_replicas` columns which are useful to check/alert when some replicas are down. One problem, these columns are numbers. They tell when there is a problem, but you need to further check ZooKeeper or query all the nodes to detect what exact replicas (hosts) are down/inactive/have problems.

**Describe the solution you'd like**

Add a replicas column maybe as a map which would contain the replica name, and it's status. Or, add 2 array columns with `replica_names` and `active_replica_names`

**Alternative**

Something along the line

```sql
select path, value from system.zookeeper where path IN (
    select concat(path, '/', name) from system.zookeeper where path in (select concat(zookeeper_path, '/replicas') from system.replicas)
)
and name = 'is_active'
```
Strings replicas = zookeeper->getChildren(fs::path(zookeeper_path) / "replicas");
    std::vector<zkutil::ZooKeeper::FutureGet> futures;
    for (const String & source_replica_name : replicas)
    {
        
        if (source_replica_name == replica_name)
            continue;
        String source_replica_path = fs::path(zookeeper_path) / "replicas" / source_replica_name;
        
        
        futures.emplace_back(zookeeper->asyncTryGet(fs::path(source_replica_path) / "is_lost"));
        futures.emplace_back(zookeeper->asyncTryGet(fs::path(source_replica_path) / "log_pointer"));
        futures.emplace_back(zookeeper->asyncTryGet(fs::path(source_replica_path) / "queue"));
    }
    
    for (auto & future : futures)
        future.wait();
    Strings log_entries = zookeeper->getChildren(fs::path(zookeeper_path) / "log");
    size_t max_log_entry = 0;
    if (!log_entries.empty())
    {
        String last_entry = *std::max_element(log_entries.begin(), log_entries.end());
        max_log_entry = parse<UInt64>(last_entry.substr(strlen("log-")));
    }
    
    ++max_log_entry;
    size_t min_replication_lag = std::numeric_limits<size_t>::max();
    String source_replica;