**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.
{
    if (!disk || !disk->supportZeroCopyReplication())
        return std::nullopt;
    return getZeroCopyPartPath(*getSettings(), toString(disk->getDataSourceDescription().type), getTableSharedID(), part_name, zookeeper_path)[0];
}
std::optional<ZeroCopyLock> StorageReplicatedMergeTree::tryCreateZeroCopyExclusiveLock(const String & part_name, const DiskPtr & disk)
{
    if (!disk || !disk->supportZeroCopyReplication())
        return std::nullopt;
    zkutil::ZooKeeperPtr zookeeper = tryGetZooKeeper();
    if (!zookeeper)
        return std::nullopt;
    String zc_zookeeper_path = *getZeroCopyPartPath(part_name, disk);
    
    zookeeper->createAncestors(zc_zookeeper_path);
    zookeeper->createIfNotExists(zc_zookeeper_path, "");
    
    ZeroCopyLock lock(zookeeper, zc_zookeeper_path);
    if (lock.lock->tryLock())
        return lock;
    else
        return std::nullopt;
}
String StorageReplicatedMergeTree::findReplicaHavingPart(