Once password reset is done, send a notification email to the user

[begedin]

Problem

This is just additional security that a lot of sites have.

Once the user successfully resets their password, they will be sent an email notifying them of this process being done, with a link to request another reset in case "someone else did this".

The email should contain something like:

Subject: Your password on codecorps.org has been reset

Your password on codecorps.org has been reset.

If you did not do this, please click here (password reset link) to reset it again.

If this was done by you, then feel free to ignore this email.

Subtasks

• on successful password reset (when the endpoint in Add a POST /password/reset endpoint #731 returns an OK), generate and send the email above
• add tests to ensure this happens
• test the email as well

@joshsmith I would like to stress that this is purely optional and not something that should in any way be considered a prerequisite to label #498 as complete, but it is something that some sites do, so I wanted to have an issue for it.

References

Progress on: #498