Optional email notifications on issues #41
Description
Let guests opt-in for notifications on request failures, e.g. downtime or token failures or unsupported address.
So this by encoding an email in the query params.
Use a bucket to only send like 100 mails daily and only 1 mail daily per email. Use a hashset or hashmap to encode that anonymously.
Might need to shorten the url to keep google calendar working. Some quick wins can be in subdomain (r.brechtserckx.be), path ('/g'), enums ('relative'). Can probably also make some more elaborate encoding of the query params