[feature]: Add Resend API key section on setup Email

[THUILLIERColin]

Is there an existing issue for this?

• I have searched the existing issues

Summary

Add a dedicated section in the email setup to input a Resend API key. This feature will allow users to seamlessly use Resend as an alternative to traditional SMTP servers for sending emails.

Why should this be worked on?

Currently, Plane only supports SMTP server configurations for email functionality. Many users prefer using services like Resend due to their simplicity and reliability. Adding this feature will provide more flexibility to users and improve the platform's adaptability for different email sending needs.