**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.
const StoragePtr & source_table, const ASTPtr & partition, bool replace, ContextPtr query_context)
{
    
    auto lock1 = lockForShare(query_context->getCurrentQueryId(), query_context->getSettingsRef().lock_acquire_timeout);
    auto lock2 = source_table->lockForShare(query_context->getCurrentQueryId(), query_context->getSettingsRef().lock_acquire_timeout);
    auto storage_settings_ptr = getSettings();
    auto source_metadata_snapshot = source_table->getInMemoryMetadataPtr();
    auto metadata_snapshot = getInMemoryMetadataPtr();
    Stopwatch watch;
    MergeTreeData & src_data = checkStructureAndGetMergeTreeData(source_table, source_metadata_snapshot, metadata_snapshot);
    String partition_id = getPartitionIDFromQuery(partition, query_context);
    
    DataPartsVector src_all_parts = src_data.getVisibleDataPartsVectorInPartition(query_context, partition_id);
    LOG_DEBUG(log, "Cloning {} parts", src_all_parts.size());
    static const String TMP_PREFIX = "tmp_replace_from_";
    auto zookeeper = getZooKeeper();
    
    for (size_t retry = 0; retry < 1000; ++retry)
    {
        DataPartsVector src_parts;
        MutableDataPartsVector dst_parts;
        std::vector<scope_guard> dst_parts_locks;
        Strings block_id_paths;
        Strings part_checksums;