Log In a User (Feature 0)

[AmusedPocket]

Logs in a current user with valid credentials and returns the current user's information.

• [x] Successful response includes the user's id, firstName, lastName, and email
• [x] Error response with status 401 is given when invalid credentials are given
• [x] Error response with status 400 is given when body validations for the email, firstName, or lastName are violated