Outgoing email logging improvements

[sergei-maertens]

We support sending custom email headers in all emails sent by Open Forms. Currently, this is only used for registration emails. See

open-forms/src/openforms/emails/constants.py

Line 4 in dd38e63

X_OF_CONTENT_TYPE_HEADER = "X-OF-Content-Type"

While debugging a production environment to figure out what type of emails were sent, I had to search on the content of the email which is fragile because different forms can use completely different templates rather than a single global configuration. This would've been easier if the registration emails would have been properly tagged with the custom headers so I could filter on this header instead (I was able to exclude registration emails this way).

Additionally, there's a typo in the content type for the Submission model - the app label is singular instead of plural.

Tasks

• Ensure that custom email headers are used for confirmation emails
• Ensure that custom email headers are used for cosign request emails
• Fix content type for submissions in email constants

[viktorvanwijk]

Currently, this is only used for registration emails

and

This would've been easier if the registration emails would have been properly tagged with the custom headers

seem to be contradicting each other. In the code I can find usages of EmailContentTypeChoices.registration, but NOT EmailContentTypeChoices.confirmation and EmailContentTypeChoices.cosign_confirmation. Shouldn't 'registration' be 'confirmation' in the task list, or am I not understanding it correctly?

[sergei-maertens]

registration emails are tagged, confirmation emails are not but should be, sorry for the confusion!