I have developed a custom module in odoo 15. I have added user access to my code and have been giving access to the admin manually ( like Settings>Users & Companies>Users>Select Admin User and choosing the access of the module to the admin user). 

Here, I want to provide the default user access to the admin, in which, as I install the custom module, the admin user has the access to the module, as it happens in the sales module. In the sales module, as we install the module the admin user gets the user access as administrator by default.