**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'
```
MutableDataPartPtr part;
    DataPartsVector replaced_parts;
    auto write_part_log = [&] (const ExecutionStatus & execution_status)
    {
        writePartLog(
            PartLogElement::DOWNLOAD_PART, execution_status, stopwatch.elapsed(),
            part_name, part, replaced_parts, nullptr);
    };
    std::function<MutableDataPartPtr()> get_part;
    ReplicatedMergeTreeAddress address(zookeeper->get(fs::path(source_replica_path) / "host"));
    auto timeouts = ConnectionTimeouts::getHTTPTimeouts(getContext());
    auto credentials = getContext()->getInterserverCredentials();
    String interserver_scheme = getContext()->getInterserverScheme();
    get_part = [&, address, timeouts, interserver_scheme, credentials]()
    {
        if (interserver_scheme != address.scheme)
            throw Exception("Interserver schemes are different: '" + interserver_scheme
                + "' != '" + address.scheme + "', can't fetch part from " + address.host,
                ErrorCodes::INTERSERVER_SCHEME_DOESNT_MATCH);
        return fetcher.fetchPart(
            metadata_snapshot, getContext(), part_name, source_replica_path,
            address.host, address.replication_port,
            timeouts, credentials->getUser(), credentials->getPassword(),
            interserver_scheme, replicated_fetches_throttler, false, "", nullptr, true,
            replaced_disk);
    };
    try
    {
        part = get_part();
        if (part->volume->getDisk()->getName() != replaced_disk->getName())