**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();
    zookeeper->createAncestors(zookeeper_path);
    for (size_t i = 0; i < 1000; ++i)
    {
        
        if (zookeeper->exists(zookeeper_path + "/replicas"))
        {
            LOG_DEBUG(log, "This table {} is already created, will add new replica", zookeeper_path);
            return false;
        }
        
        if (zookeeper->exists(zookeeper_path + "/dropped"))
        {
            
            
            
            LOG_WARNING(log, "Removing leftovers from table {} (this might take several minutes)", zookeeper_path);
            String drop_lock_path = zookeeper_path + "/dropped/lock";
            Coordination::Error code = zookeeper->tryCreate(drop_lock_path, "", zkutil::CreateMode::Ephemeral);
            if (code == Coordination::Error::ZNONODE || code == Coordination::Error::ZNODEEXISTS)
            {
                LOG_WARNING(log, "The leftovers from table {} were removed by another replica", zookeeper_path);
            }
            else if (code != Coordination::Error::ZOK)
            {
                throw Coordination::Exception(code, drop_lock_path);