Feat: Add automatic newsletter sending feature on subscribing

[vansh-codes]

Describe the feature

When user subscribes to newsletter, the user gets an email which is sent automatically through the backend.

This welcome email serves several important purposes:

• Welcome and Acknowledge: It thanks the new subscriber for joining the mailing list and acknowledges their subscription.
• Introduction: It introduces the brand or organization, providing a brief overview of what the subscriber can expect from the newsletter.
• Set Expectations: It outlines the type of content, frequency of emails, and any other relevant details about what the subscriber can expect.
• Engagement: It encourages further engagement, such as following the brand on social media, visiting the website, or exploring popular content.
• Personalization: It often includes personalized content, making the subscriber feel valued and appreciated.

Assign this under GSSoC'24. Thank you!

Add ScreenShots

Backend feature

Record

• [X] I agree to follow this project's Code of Conduct
• [X] I'm a GSSOC'24 contributor
• [X] I want to work on this issue

[github-actions[bot]]

Thank you for creating this issue! 🎉 We'll look into it as soon as possible. In the meantime, please make sure to provide all the necessary details and context. If you have any questions or additional information, feel free to add them here. Your contributions are highly appreciated! 😊

You can also check our CONTRIBUTING.md for guidelines on contributing to this project.