Make cloud email domain configurable (#4982)

# What this PR does

Fixes https://github.com/grafana/oncall-private/issues/2889

## Checklist

- [x] Unit, integration, and e2e (if applicable) tests updated
- [x] Documentation added (or `pr:no public docs` PR label added if not
required)
- [x] Added the relevant release notes label (see labels prefixed w/
`release:`). These labels dictate how your PR will
    show up in the autogenerated release notes.

engine/apps/email/tasks.py

@@ -21,7 +21,7 @@ def get_from_email(user):
         return live_settings.EMAIL_FROM_ADDRESS
 
     if settings.LICENSE == settings.CLOUD_LICENSE_NAME:
-        return "oncall@{}.grafana.net".format(user.organization.stack_slug)
+        return "oncall@{}.{}".format(user.organization.stack_slug, settings.EMAIL_FROM_DOMAIN)
 
     return live_settings.EMAIL_HOST_USER
 

engine/settings/base.py

@@ -844,6 +844,7 @@ EMAIL_PORT = getenv_integer("EMAIL_PORT", 587)
 EMAIL_USE_TLS = getenv_boolean("EMAIL_USE_TLS", True)
 EMAIL_USE_SSL = getenv_boolean("EMAIL_USE_SSL", False)
 EMAIL_FROM_ADDRESS = os.getenv("EMAIL_FROM_ADDRESS")
+EMAIL_FROM_DOMAIN = os.getenv("EMAIL_FROM_DOMAIN", "grafana.net")
 EMAIL_NOTIFICATIONS_LIMIT = getenv_integer("EMAIL_NOTIFICATIONS_LIMIT", 200)
 
 EMAIL_BACKEND_INTERNAL_ID = 8