[LLSC-20] Implement Skeleton Email Service

[Mayank808]

Notion ticket link

Setup Basic Email System

Implementation description

Setup a quick skeleton for email service with interfaces and classes defined. Will be implementing actual functionality in next pr. Created a test endpoint to ensure that implementation of skeleton classes is done properly just need to add actual logic.

Steps to test

1. Can run backend properly
2. Hit the new test email API. Can check fast API docs for params/requirements

What should reviewers focus on?

• Interface definitions other functionalities that we may ned

Checklist

• My PR name is descriptive and in imperative tense
• My commit messages are descriptive and in imperative tense. My commits are atomic and trivial commits are squashed or fixup'd into non-trivial commits
• I have run the appropriate linter(s)
• I have requested a review from the PL, as well as other devs who have background knowledge on this PR or who will be building on top of this PR

[mslwang]

LGTM! Given that the ticket includes using an email provider, we can either split this PR into a separate ticket or have the email provider implementation under the same ticket.

[EdmondLi1]

LGTM