**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.
/** Wait until all replicas, including this, execute the specified action from the log.
      * If replicas are added at the same time, it can not wait the added replica.
      *
      * Waits for inactive replicas no more than wait_for_inactive_timeout.
      * Returns list of inactive replicas that have not executed entry or throws exception.
      *
      * NOTE: This method must be called without table lock held.
      * Because it effectively waits for other thread that usually has to also acquire a lock to proceed and this yields deadlock.
      */
    void waitForAllReplicasToProcessLogEntry(const String & table_zookeeper_path, const ReplicatedMergeTreeLogEntryData & entry,
                                             Int64 wait_for_inactive_timeout, const String & error_context = {});
    Strings tryWaitForAllReplicasToProcessLogEntry(const String & table_zookeeper_path, const ReplicatedMergeTreeLogEntryData & entry,
                                                   Int64 wait_for_inactive_timeout);
    /** Wait until the specified replica executes the specified action from the log.
      * NOTE: See comment about locks above.
      */
    bool tryWaitForReplicaToProcessLogEntry(const String & table_zookeeper_path, const String & replica_name,
                                            const ReplicatedMergeTreeLogEntryData & entry, Int64 wait_for_inactive_timeout = 0);
    
    void waitForLogEntryToBeProcessedIfNecessary(const ReplicatedMergeTreeLogEntryData & entry, ContextPtr query_context, const String & error_context = {});
    
    void assertNotReadonly() const;
    
    
    
    
    bool getFakePartCoveringAllPartsInPartition(const String & partition_id, MergeTreePartInfo & part_info,
                                                std::optional<EphemeralLockInZooKeeper> & delimiting_block_lock, bool for_replace_range = false);
    
    mutable std::unordered_set<std::string> existing_nodes_cache;