**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'
```
#include <Core/Defines.h>
#include "Common/hex.h"
#include <Common/Macros.h>
#include <Common/StringUtils/StringUtils.h>
#include <Common/ThreadPool.h>
#include <Common/ZooKeeper/KeeperException.h>
#include <Common/ZooKeeper/Types.h>
#include <Common/escapeForFileName.h>
#include <Common/formatReadable.h>
#include <Common/thread_local_rng.h>
#include <Common/typeid_cast.h>
#include <Storages/AlterCommands.h>
#include <Storages/PartitionCommands.h>
#include <Storages/ColumnsDescription.h>
#include <Storages/StorageReplicatedMergeTree.h>
#include <Storages/MergeTree/IMergeTreeDataPart.h>
#include <Storages/MergeTree/MergeList.h>
#include <Storages/MergeTree/MergedBlockOutputStream.h>
#include <Storages/MergeTree/PinnedPartUUIDs.h>