Move SMTP credentials to external environment variable

[pablodiegoss]

In the users/services/email_service.py we have an explicit set of email and password which will send the recover-password e-mail in the platform:

That should be replaced by an environment variable and put on the src/.envs folder, there on each file under the Django section.
This value for this variable will be set later by the CI and on each environment that Jandig runs.