[#163901873] Send appropriate message to the user

[Sammuel09]

What does this PR do?

Fixes a bug on the signup controller.

Description of Task to be completed?

• Sends an appropriate message back to the user if the username or email is already in the database
• Includes tests for the feature

How should this be manually tested?

• Use git fetch to clone this branch.
• Switch to this branch in your machine.
• Run npm run dev to start the server.
• Sign up a user at http://localhost:3000/api/v1/auth/signup.
• Try to sign up the same user with the same credentials.
• The appropriate message is sent back to the user if the email or username has been taken.

What are the relevant pivotal tracker stories?

Link to Pivotal Tracker

[rafmme]

Is this if(!foundUser) {} statement necessary? If the user doesn't exist yet that means the new user can then sign up with the data not give 404 error

[Sammuel09]

Thanks for this comment, rafmme. Actually, this check is necessary because I need to make sure this user is in the database record or not. This is because only a user whose record has been previously created should be able to get a new verification email.