**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'
```
const String & zookeeper_path_,
    const String & replica_name_,
    bool attach,
    const StorageID & table_id_,
    const String & relative_data_path_,
    const StorageInMemoryMetadata & metadata_,
    ContextMutablePtr context_,
    const String & date_column_name,
    const MergingParams & merging_params_,
    std::unique_ptr<MergeTreeSettings> settings_,
    bool has_force_restore_data_flag,
    bool allow_renaming_)
    : MergeTreeData(table_id_,
                    relative_data_path_,
                    metadata_,
                    context_,
                    date_column_name,
                    merging_params_,
                    std::move(settings_),
                    true,                   
                    attach,
                    [this] (const std::string & name) { enqueuePartForCheck(name); })
    , zookeeper_name(extractZooKeeperName(zookeeper_path_))
    , zookeeper_path(extractZooKeeperPath(zookeeper_path_))
    , replica_name(replica_name_)
    , replica_path(fs::path(zookeeper_path) / "replicas" / replica_name_)