Deprecation: opt-out from config file email (#10440)
* Deprecation: opt-out from config file email
This is the minimal version without spending too much time.
If we are fine with this, we can merge it for now and grow from here.
It does not look too complex, to keep or to remove it later :)
* Make the field nullable
* Update text from the email to mention opt-out
* Minor copy feedback
