**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.
{
        String zookeeper_node = fs::path(zc_zookeeper_path) / id / replica_name;
        LOG_TRACE(log, "Set zookeeper persistent lock {}", zookeeper_node);
        createZeroCopyLockNode(
            zookeeper, zookeeper_node, zkutil::CreateMode::Persistent,
            replace_existing_lock, path_to_set_hardlinked_files, hardlinks);
    }
}
std::pair<bool, NameSet> StorageReplicatedMergeTree::unlockSharedData(const IMergeTreeDataPart & part) const
{
    if (!part.data_part_storage || !part.isStoredOnDisk())
        return std::make_pair(true, NameSet{});
    if (!part.data_part_storage || !part.data_part_storage->supportZeroCopyReplication())
        return std::make_pair(true, NameSet{});
    
    if (part.data_part_storage->exists(IMergeTreeDataPart::FILE_FOR_REFERENCES_CHECK))
    {
        auto ref_count = part.data_part_storage->getRefCount(IMergeTreeDataPart::FILE_FOR_REFERENCES_CHECK);
        if (ref_count > 0) 
            return std::make_pair(false, NameSet{});
    }
    else
    {
        
        return std::make_pair(true, NameSet{});
    }
    return unlockSharedDataByID(part.getUniqueId(), getTableSharedID(), part.name, replica_name, part.data_part_storage->getDiskType(), getZooKeeper(), *getSettings(), log,
        zookeeper_path);
}
std::pair<bool, NameSet> StorageReplicatedMergeTree::unlockSharedDataByID(