Feat mail support

[Aaditya-Singh78]

Fixes #9113

Short description of what this resolves:

Mail support resolves the integration of email functionality within an application, facilitating communication with users, administrators, or other stakeholders through email channels. It enables sending and receiving emails for various purposes such as account management, notifications, alerts, and promotional campaigns. The MailingList model specifically addresses managing email subscriptions, allowing users to subscribe to mailing lists and receive updates or newsletters from the application. This feature enhances user engagement, facilitates information dissemination, and strengthens communication channels between the application and its users.

Changes proposed in this pull request:

• Added a Mailing List model to manage email subscriptions.
• Included an email field with constraints unique, blank, and null set to True.
• Added a subscribed_at field to track the subscription timestamp.
• Implemented a str method to return the email address if available, otherwise, a generic message indicating no email specified.

Checklist

• I have read the Contribution & Best practices Guide and my PR follows them.
• My branch is up-to-date with the Upstream development branch.
• The unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

• All the functions created/modified in this PR contain relevant docstrings.