feat(api, app): Enhance Email Change Process with Confirmation Link and Token

[ThomasDos]

• Implemented a confirmation link and token system for secure email changes.
• Introduced two new email templates to improve the user experience during email changes.
• Notified the previous email address regarding the upcoming change for transparency.
• Sent a confirmation email to the new address, ensuring a user-friendly confirmation process.
• Generated a token for frontend-initiated confirmation and user login.