**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 MutationCommands & commands, ContextPtr query_context, const zkutil::ZooKeeperPtr & zookeeper) const
{
    const std::set<String> mutation_affected_partition_ids = getPartitionIdsAffectedByCommands(commands, query_context);
    if (mutation_affected_partition_ids.size() == 1)
    {
        const auto & affected_partition_id = *mutation_affected_partition_ids.cbegin();
        auto block_number_holder = allocateBlockNumber(affected_partition_id, zookeeper);
        if (!block_number_holder.has_value())
            return {};
        auto block_number = block_number_holder->getNumber();  
        return {{{affected_partition_id, block_number}}, std::move(block_number_holder)};
    }
    else
    {
        
        EphemeralLocksInAllPartitions lock_holder(
            fs::path(zookeeper_path) / "block_numbers", "block-", fs::path(zookeeper_path) / "temp", *zookeeper);
        PartitionBlockNumbersHolder::BlockNumbersType block_numbers;
        for (const auto & lock : lock_holder.getLocks())
        {
            if (mutation_affected_partition_ids.empty() || mutation_affected_partition_ids.count(lock.partition_id))
                block_numbers[lock.partition_id] = lock.number;
        }
        return {std::move(block_numbers), std::move(lock_holder)};
    }
}
void StorageReplicatedMergeTree::alter(