[Feature]: Add Mail service for newsletter using nodemailer

[Debajyoti-3]

📌 Is your feature request related to a problem?

Actully I want to add Email greeting/notification functionality when an user subscribe newsletter

💡 Describe the Solution

Plan to add nodemailer service for email service. Suppose an user subscribe the newsletter by putting his/her email id, then by adding this feature a mail from civix will go to the user's inbox where mail will be "Congrats for subscribing our newslteer"

I waant to work on this, please assign me this @HarshS16

[github-actions]

Thank you for raising this issue!

We'll review it as soon as possible. We truly appreciate your contributions! ✨

Meanwhile make sure you've visited the README.md, CONTRIBUTING.md, and CODE_OF_CONDUCT.md before creating a PR for this. Also, please do NOT create a PR until this issue has been assigned to you. 😊