feat(self-extension rights management): implement user self-extension rights system

[mitaahs]

• Add a default value in configuration files to support the new rights management system
• Add a disable_extend field for new users
• Add enforcement mechanisms to validate self-extension rights during extension requests, ensuring only authorized users can extend their accounts
• Add a button on the user page for administrators to toggle self-extension rights
• Exclude the extend button for users without self-extension rights
• Add a dedicated email template for users without self-extend rights approaching account expiration
• Add verification logic to send the appropriate expiration email based on user rights status

Resolves : #618