cPanel limit access APACHE

 how can i limit access APACHE only in "domaine.dz" ?

Not necessarily through Apache, however, php-fpm would do this if this domain was set to use the PHP-FPM handler. Activating fpm for this domain would allow them to limit the amount of traffic this user can have concurrently through the max_children variable. Information on this variable will be below.
PHP-FPM Performance Tuning Basics

I see that the PHP-FPM php handler isn't enabled or installed on this server. So what I'd suggest if you'd like to do this is to install the PHP-FPM handler and set this domain to use this:
How to install PHP-FPM
How to change PHP handlers
 

How can i add performance of my APACHE, without disrupting mail which is important then to the APACHE ?

I see that the server's Apache installation reached the maxrequestworkers variable which prevented traffic for the server from being processed. The MaxRequestWorkers variable limits the amount of concurrent processes apache is handling at one time, currently, this is set to be 150:

You can update the MaxRequestWorkers value in WHM with the following steps:

1. Log in to WHM as the root user.
2. Navigate to Home »Service Configuration »Apache Configuration »Global Configuration.
3. Update the "Max Request Worker" value.
4. Set the ServerLimit value to something larger than MaxRequestWorkers
5. Select Save.

Updating this variable will allow apache to handle more concurrent processes which will prevent your websites from going down if the same amount of traffic occurs again.
Tuning MaxRequestWorkers for Apache