**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'
```
zkutil::ZooKeeperPtr tryGetZooKeeper() const;
    zkutil::ZooKeeperPtr getZooKeeper() const;
    void setZooKeeper();
    
    std::atomic_bool is_readonly {false};
    
    bool has_metadata_in_zookeeper = true;
    static constexpr auto default_zookeeper_name = "default";
    String zookeeper_name;
    String zookeeper_path;
    String replica_name;
    String replica_path;
    /** /replicas/me/is_active.
      */
    zkutil::EphemeralNodeHolderPtr replica_is_active_node;
    /** Is this replica "leading". The leader replica selects the parts to merge.
      * It can be false only when old ClickHouse versions are working on the same cluster, because now we allow multiple leaders.
      */
    std::atomic<bool> is_leader {false};
    zkutil::LeaderElectionPtr leader_election;
    InterserverIOEndpointPtr data_parts_exchange_endpoint;
    MergeTreeDataSelectExecutor reader;
    MergeTreeDataWriter writer;
    MergeTreeDataMergerMutator merger_mutator;
    MergeStrategyPicker merge_strategy_picker;
    /** The queue of what needs to be done on this replica to catch up with everyone. It is taken from ZooKeeper (/replicas/me/queue/).
     * In ZK entries in chronological order. Here it is not necessary.
     */
    ReplicatedMergeTreeQueue queue;
    std::atomic<time_t> last_queue_update_start_time{0};