Feat: Implement email integration

[jkarenzi]

What does this PR do?

This PR implements email integration. The functionality of sending emails is used in email verification and two factor authentication.

Description of the task to be completed

• Email integration with mailgun or any other provider
• Implement email verification as an additional step after signing up. Unverified users should login but shouldn't be able to access the majority of the app's features
• Implement 2FA upon login, for users who requested that additional step
• Write appropriate documentation for resulting endpoints
• Implement appropriate error handling and responses
• Write comprehensive unit tests

How can this be manually tested?

• Upon signup, a new user should receive an email, asking them to verify their email
• Upon login, if 2FA is enabled, a user will receive a code on their email, which they will use to continue with the authentication process

Swagger documentation screenshot

Test screenshot

What are the relevant pivotal trackers/story id?

• Feat: Email verification and Two factor Authentication #4

[codecov]

Codecov Report

Attention: Patch coverage is 89.52381% with 11 lines in your changes missing coverage. Please review.

Project coverage is 92.50%. Comparing base (c1d809f) to head (55fee53).

Files	Patch %	Lines
src/utils/sendEmail.ts	45.00%	10 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop       #8      +/-   ##
===========================================
- Coverage   100.00%   92.50%   -7.50%     
===========================================
  Files           10       13       +3     
  Lines           84      200     +116     
  Branches         5       16      +11     
===========================================
+ Hits            84      185     +101     
- Misses           0       14      +14     
- Partials         0        1       +1     

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