**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 metadata_zk_path = fs::path(txn->getDatabaseZooKeeperPath()) / "metadata" / escapeForFileName(table_id.table_name);
            auto ast = DatabaseCatalog::instance().getDatabase(table_id.database_name)->getCreateTableQuery(table_id.table_name, query_context);
            applyMetadataChangesToCreateQuery(ast, future_metadata);
            ops.emplace_back(zkutil::makeSetRequest(metadata_zk_path, getObjectDefinitionFromCreateQuery(ast), -1));
        }
        Coordination::Responses results;
        Coordination::Error rc = zookeeper->tryMulti(ops, results);
        
        
        
        partition_block_numbers_holder.reset();
        if (rc == Coordination::Error::ZOK)
        {
            if (have_mutation)
            {
                
                String alter_path = dynamic_cast<const Coordination::CreateResponse &>(*results[alter_path_idx]).path_created;
                alter_entry->znode_name = alter_path.substr(alter_path.find_last_of('/') + 1);
                
                String mutation_path = dynamic_cast<const Coordination::CreateResponse &>(*results[mutation_path_idx]).path_created;
                mutation_znode = mutation_path.substr(mutation_path.find_last_of('/') + 1);
            }
            else
            {
                
                String alter_path = dynamic_cast<const Coordination::CreateResponse &>(*results[alter_path_idx]).path_created;
                alter_entry->znode_name = alter_path.substr(alter_path.find_last_of('/') + 1);
            }