feat: Sending mails on newsletter subscription

[Ayesha-Siddiqua88]

I want to implement a feature where a mail is sent to the user when they subscribe to the newsletter. I would implement this feature with the help of emailjs.
The mail can say something like "Thankyou for subscribing to bigohhh newsletter. Stay tuned for more updates.....".

@omrajsharma , please assign this issue to me under GSSoC'24