**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 (table_shared_id != UUIDHelpers::Nil)
        throw Exception(ErrorCodes::LOGICAL_ERROR, "Table shared id already initialized");
    zkutil::ZooKeeperPtr zookeeper = getZooKeeper();
    String zookeeper_table_id_path = fs::path(zookeeper_path) / "table_shared_id";
    String id;
    if (!zookeeper->tryGet(zookeeper_table_id_path, id))
    {
        UUID table_id_candidate;
        auto local_storage_id = getStorageID();
        if (local_storage_id.uuid != UUIDHelpers::Nil)
            table_id_candidate = local_storage_id.uuid;
        else
            table_id_candidate = UUIDHelpers::generateV4();
        id = toString(table_id_candidate);
        auto code = zookeeper->tryCreate(zookeeper_table_id_path, id, zkutil::CreateMode::Persistent);
        if (code == Coordination::Error::ZNODEEXISTS)
        { 
            id = zookeeper->get(zookeeper_table_id_path);
        }
        else if (code != Coordination::Error::ZOK)
        {
            throw zkutil::KeeperException(code, zookeeper_table_id_path);
        }
    }
    table_shared_id = parseFromString<UUID>(id);
}
std::optional<String> StorageReplicatedMergeTree::tryGetTableSharedIDFromCreateQuery(const IAST & create_query, const ContextPtr & global_context)