**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 (!mutations_sync)
        return;
    
    auto zookeeper = getZooKeeper();
    Strings replicas;
    if (mutations_sync == 2) 
    {
        replicas = zookeeper->getChildren(fs::path(zookeeper_path) / "replicas");
        
        for (auto it = replicas.begin(); it != replicas.end(); ++it)
        {
            if (*it == replica_name)
            {
                std::iter_swap(it, replicas.begin());
                break;
            }
        }
    }
    else if (mutations_sync == 1) 
        replicas.push_back(replica_name);
    waitMutationToFinishOnReplicas(replicas, znode_name);
}
std::vector<MergeTreeMutationStatus> StorageReplicatedMergeTree::getMutationsStatus() const