Prevent emails from going straight to junk-email folder

[Rian501]

(Research and implement) possibly some kind of whitelisting for the sendgrid/firebase function to keep the glean requests from going to the junk/spam folder of email.

[coreyar]

To solve this we will need to verify the domain the emails are being sent from.
https://sendgrid.com/docs/ui/account-and-settings/how-to-set-up-domain-authentication/