feat: add Apple authentication functionality

This commit introduces the ability to register and authenticate using an Apple account. Multiple frontend files have been created or modified including 'Apple.js', 'Button.css', 'Button.js', and 'locale.xml'.

New classes have been defined in 'Apple.js' and 'Button.js' to enable the Apple authentication function. The CSS file and locale.xml were also updated to enhance the frontend experience for the users.

Backend files 'Button.php' and 'Registrar.php' were also adjusted to accommodate the new functionality. Changes include the addition of a button for Apple authentication and modifications in the Registrar class for Apple account registration.