Send mail for auto-disable events (Z#23124771)

[ser8phin]

Inform organizers about automatic disabling of mollie because of failing token refresh

[ser8phin]

Food for thought: It might be better to contact the primary contact?

[raphaelm]

Yeah, "who to contact" is my main concern here:

• primary contact → not really possible, as that is a concept specific to pretix hosted
• event contact (like you did) → not great, it's more meant to be contacted by customers
• all users with admin permission to the event → pretty noisy

we lack a proper framework to do notifications for something like this :\ the best way would probably to go through the proper "user notification" framework with default-on for new users (like we do for external refunds)?

[ser8phin]

Will be fixed differently in another branch