> (you don't have to strictly follow this form)

**Use case**

Sometimes, for really sophisticated scenarios it can be hard to control the amount of in-progress backups run externally. For the purpose of simpler control we can introduce server-level setting which disallows running concurrent backups of any type. 

Something like this in `config.xml` (enabled by default):
`<allow_concurrent_backups>true</allow_concurrent_backups>`

**Describe the solution you'd like**

It's important that backups can be executed in distributed way on multiple servers. Need to take it into account.

**Describe alternatives you've considered**
External check of `system.backups` table, but it can be complex.

{
                RestorerFromBackup restorer{restore_query->elements, restore_settings, restore_coordination,
                                            backup, context};
                data_restore_tasks = restorer.run(RestorerFromBackup::RESTORE);
            }
            
            restoreTablesData(std::move(data_restore_tasks), restores_thread_pool);
            
            restore_coordination->setStage(restore_settings.host_id, Stage::COMPLETED, "");
        }
        LOG_INFO(log, "Restored from {} {} successfully", (restore_settings.internal ? "internal backup" : "backup"), backup_name_for_logging);
        setStatus(restore_id, BackupStatus::RESTORED);
    }
    catch (...)
    {
        
        if (called_async)
        {
            tryLogCurrentException(log, fmt::format("Failed to restore from {} {}", (restore_settings.internal ? "internal backup" : "backup"), backup_name_for_logging));
            setStatusSafe(restore_id, BackupStatus::RESTORE_FAILED);
            sendCurrentExceptionToCoordination(restore_coordination, restore_settings.host_id);
        }
        else
        {
            
            throw;
        }
    }
}
void BackupsWorker::addInfo(const OperationID & id, const String & name, bool internal, BackupStatus status)