The References header is an ordered list of mails, and some clients
only look at the last mail in the list to determine to which mail the
mail is in reply to.
Therefore, to be a less obtrusive as possible, put the fallback
address first.
Some info about the reply key lookup in the References header:
https://docs.gitlab.com/ee/administration/reply_by_email.html#how-it-works
Other improvements:
- Ensure slash commands autocomplete doesn't break when noteable_type is not given
- Slash commands: improve autocomplete behavior and /due command
- We don't display slash commands for note edit forms.
- Add tests for reply by email with slash commands
- Be sure to execute slash commands after the note creation in Notes::CreateService
Signed-off-by: Rémy Coutable <remy@rymai.me>