**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 String & table_zookeeper_path, const ReplicatedMergeTreeLogEntryData & entry, Int64 wait_for_inactive_timeout, const String & error_context)
{
    Strings unfinished_replicas = tryWaitForAllReplicasToProcessLogEntry(table_zookeeper_path, entry, wait_for_inactive_timeout);
    if (unfinished_replicas.empty())
        return;
    throw Exception(ErrorCodes::UNFINISHED, "{}Timeout exceeded while waiting for replicas {} to process entry {}. "
                    "Probably some replicas are inactive", error_context, fmt::join(unfinished_replicas, ", "), entry.znode_name);
}
void StorageReplicatedMergeTree::waitForLogEntryToBeProcessedIfNecessary(const ReplicatedMergeTreeLogEntryData & entry, ContextPtr query_context, const String & error_context)