**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.
{
    CheckResults results;
    DataPartsVector data_parts;
    if (const auto & check_query = query->as<ASTCheckQuery &>(); check_query.partition)
    {
        String partition_id = getPartitionIDFromQuery(check_query.partition, local_context);
        data_parts = getVisibleDataPartsVectorInPartition(local_context, partition_id);
    }
    else
        data_parts = getVisibleDataPartsVector(local_context);
    for (auto & part : data_parts)
    {
        try
        {
            results.push_back(part_check_thread.checkPart(part->name));
        }
        catch (const Exception & ex)
        {
            results.emplace_back(part->name, false, "Check of part finished with error: '" + ex.message() + "'");
        }
    }
    return results;
}
void StorageReplicatedMergeTree::checkBrokenDisks()