Write a file `uuid` in server's data directory that contains random UUID, generated at startup if file does not exist.

It will be used for several purposes:
- to anonymously identify server in Sentry (currently Sentry is unusable);
- (possible future usage) to identify server in ensemble.

@tavplubix comments?
global_context->setMaxTableSizeToDrop(config->getUInt64("max_table_size_to_drop"));
            if (config->has("max_partition_size_to_drop"))
                global_context->setMaxPartitionSizeToDrop(config->getUInt64("max_partition_size_to_drop"));
            if (!initial_loading)
            {
                
                
                if (config->has("zookeeper"))
                    global_context->reloadZooKeeperIfChanged(config);
                global_context->reloadAuxiliaryZooKeepersConfigIfChanged(config);
            }
            global_context->updateStorageConfiguration(*config);
            global_context->updateInterserverCredentials(*config);
        },
         false);  
    auto & access_control = global_context->getAccessControlManager();
    if (config().has("custom_settings_prefixes"))
        access_control.setCustomSettingsPrefixes(config().getString("custom_settings_prefixes"));
    
    access_control.addStoragesFromMainConfig(config(), config_path, [&] { return global_context->getZooKeeper(); });
    
    global_context->setConfigReloadCallback([&]()
    {
        main_config_reloader->reload();
        access_control.reloadUsersConfigs();
    });
    
    global_context->getProcessList().setMaxSize(config().getInt("max_concurrent_queries", 0));