Bug 33203: Add letter_code to the letter dropdown text

Bug 33203: Add letter_code to the letter dropdown text

To test:
1. Add a new notice in the Circulation module with a letter code of 'ABC'. Give the new notice a name of 'Overdue notice'.
2. Now to go Overdue notice/status triggers and look at the dropdown, notice 2 choices that both read 'Overdue notice'.
3. Apply patch and try again.
4. The new notice should now read "Overdue notice (ABC)" and should be easy to distinguish from the original.

Signed-off-by: Sally <sally.healey@cheshiresharedservices.gov.uk>
Signed-off-by: Aleisha Amohia <aleishaamohia@hotmail.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>