Set eodag items_per_page

The default items_per_page value in eodag is 20 (defined in eodag core.py). I should have missed some crucial information about how to change this limit... in eodag configuration file? I ended up changing the value in eodag core.py from 20 to 500, in order to complete my downloads. I think there should be some documentation about how to do that properly, and maybe change the default value because 20 is very low.