Add X-GitLab-NotificationReason header to note emails
What does this MR do?
Adds the X-GitLab-NotificationReason header to note emails. There are currently three reasons implemented:
- mentioned
- assigned
- own_activity
The second one doesn't apply to notes, but the other two do, so it's worth having.
See https://gitlab.com/gitlab-org/gitlab-ce/issues/63140.
Does this MR meet the acceptance criteria?
Conformity
-
Changelog entry for user-facing changes, or community contribution. Check the link for other scenarios.
Performance and Testing
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Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.