**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'
```
Coordination::Stat columns_stat_before, columns_stat_after;
            String columns_str;
            String checksums_str;
            
            
            if (!zookeeper->tryGet(fs::path(current_part_path) / "columns", columns_str, &columns_stat_before) ||
                !zookeeper->tryGet(fs::path(current_part_path) / "checksums", checksums_str) ||
                !zookeeper->exists(fs::path(current_part_path) / "columns", &columns_stat_after) ||
                columns_stat_before.version != columns_stat_after.version)
            {
                LOG_INFO(log, "Not checking checksums of part {} with replica {} because part changed while we were reading its checksums", part_name, replica);
                continue;
            }
            replica_part_header = ReplicatedMergeTreePartHeader::fromColumnsAndChecksumsZNodes(
                columns_str, checksums_str);
        }
        if (replica_part_header.getColumnsHash() != local_part_header.getColumnsHash())
        {
            LOG_INFO(log, "Not checking checksums of part {} with replica {} because columns are different", part_name, replica);
            continue;
        }
        replica_part_header.getChecksums().checkEqual(local_part_header.getChecksums(), true);
        if (replica == replica_name)
            has_been_already_added = true;
        
        
        if (absent_replicas_paths)
        {
            absent_replicas_paths->clear();
            break;