**Describe the solution you'd like**

We already can run clickhouse-server without configured ZooKeeper (the tables will start in read-only mode)
and with configured ZooKeeper, if it starts to be inaccessible at runtime (the tables will be read-only until the session is re-established).

Let's also make it possible to start up when ZooKeeper is unavailable.

**Additional context**

If that will be very hard to implement, we can consider other options:
- lazy attaching of the tables after sever start-up;
- a maintenance mode when the tables are not attached at start-up and require manual ATTACH queries.
{
    auto zookeeper = getZooKeeper();
    LOG_DEBUG(log, "Creating replica {}", replica_path);
    Coordination::Error code;
    do
    {
        Coordination::Stat replicas_stat;
        String replicas_value;
        if (!zookeeper->tryGet(zookeeper_path + "/replicas", replicas_value, &replicas_stat))
            throw Exception(ErrorCodes::ALL_REPLICAS_LOST,
                "Cannot create a replica of the table {}, because the last replica of the table was dropped right now",
                zookeeper_path);
        
        
        const String is_lost_value = replicas_stat.numChildren ? "1" : "0";
        Coordination::Requests ops;
        ops.emplace_back(zkutil::makeCreateRequest(replica_path, "",
            zkutil::CreateMode::Persistent));
        ops.emplace_back(zkutil::makeCreateRequest(replica_path + "/host", "",
            zkutil::CreateMode::Persistent));
        ops.emplace_back(zkutil::makeCreateRequest(replica_path + "/log_pointer", "",
            zkutil::CreateMode::Persistent));
        ops.emplace_back(zkutil::makeCreateRequest(replica_path + "/queue", "",
            zkutil::CreateMode::Persistent));
        ops.emplace_back(zkutil::makeCreateRequest(replica_path + "/parts", "",