**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 (!drop_range_info.isFakeDropRangePart())
                LOG_INFO(log, "Log entry {} tried to drop single part {}, but part does not exist", entry.znode_name, entry.new_part_name);
            return;
        }
    }
    if (entry.detach)
        LOG_DEBUG(log, "Detaching parts.");
    else
        LOG_DEBUG(log, "Removing parts.");
    if (entry.detach)
    {
        
        for (const auto & part : parts_to_remove)
        {
            LOG_INFO(log, "Detaching {}", part->data_part_storage->getPartDirectory());
            part->makeCloneInDetached("", metadata_snapshot);
        }
    }
    
    removePartsFromZooKeeperWithRetries(parts_to_remove);
    if (entry.detach)
        LOG_DEBUG(log, "Detached {} parts inside {}.", parts_to_remove.size(), entry.new_part_name);
    else
        LOG_DEBUG(log, "Removed {} parts inside {}.", parts_to_remove.size(), entry.new_part_name);
    
    
    parts_to_remove.clear();
    cleanup_thread.wakeup();
}
bool StorageReplicatedMergeTree::executeReplaceRange(const LogEntry & entry)