Delete non active users

[ihsaan-ullah]

@Didayolo

Description

Sometimes users create accounts and do not activate them. To keep our db clean we want to delete the non activated users who have created accounts but have not activated their accounts for more than 3 days. The auto-task will run every 24 hours to check for such accounts and will delete them

Issues this PR resolves

• Delete non activated users #1884

A checklist for hand testing

• change the time of task in base.py to maybe 5 minutes to test locally

'clean_non_activated_users': {
        'task': 'profiles.tasks.clean_non_activated_users',
        'schedule': timedelta(minutes=5),  # Run every 5 minutes
    },

• change the time of account creation in profiles/tasks.py to maybe 1 minutes to test locally

 three_days_ago = now() - timedelta(minutes=1)

• Create users and do not activate them, check that the clean_non_activated_users task runs and deletes the non-activated users

Checklist

• Code review by me
• Hand tested by me
• I'm proud of my work
• Code review by reviewer
• Hand tested by reviewer
• CircleCi tests are passing
• Ready to merge

[Didayolo]

TODO: add a check that the account has no competitions and no submissions. This is a safety measure to avoid, for instance, deleting useful accounts that got marked as inactive.