**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.
const DataPartPtr & part, std::optional<MergeTreeData::HardlinkedFiles> hardlinked_files)
{
    auto zookeeper = getZooKeeper();
    while (true)
    {
        Coordination::Requests ops;
        NameSet absent_part_paths_on_replicas;
        lockSharedData(*part, false, hardlinked_files);
        
        checkPartChecksumsAndAddCommitOps(zookeeper, part, ops, part->name, &absent_part_paths_on_replicas);
        
        if (transaction.isEmpty())
            return {};
        
        if (!absent_part_paths_on_replicas.empty())
        {
            Coordination::Requests new_ops;
            for (const String & part_path : absent_part_paths_on_replicas)
            {
                
                new_ops.emplace_back(zkutil::makeCreateRequest(part_path, "", zkutil::CreateMode::Persistent));
                new_ops.emplace_back(zkutil::makeRemoveRequest(part_path, -1));
            }