💻 Implement a request rate limiter

[TiBiBa]

Description Some routes automatically sent an e-mail. Either to ourselves, or to a user (for example for the 'reset password'). This introduces risks as there is no limit on the amount of times a user can make this request. We should implement either a username, e-mail and/or ip-address rate limiter.

https://flask-limiter.readthedocs.io/en/stable/