Use email service in password recovery

[jamcunha]

As #82 wasn't ready yet, we did not use the email service in the password recovery method done in #113.

Regarding testing the password recovery request, we should:

• Check that we do not send an email nor generate the token if the account does not exist.
• Check that we generate and send the token if the account exists.

We can use mocks to confirm that functions are being called instead of sending actual emails.

Regarding testing the processing of the request part, additional tests should not be needed, but a refactor is necessary to receive the token for the test.

[BrunoRosendo]

You can check how it's being done in NIJobs as I believe it's pretty well implemented: https://github.com/NIAEFEUP/nijobs-be/blob/4ab4f74789c0568ecfa8a4f3c4c618ae13df5ad3/test/end-to-end/auth.js#L243