Add Patron Barcode token to CRUD staff slip templates

Need to add Requester barcode t token to staff slips templates (http://folio-snapshot-stable.aws.indexdata.com/settings/circulation/staffslips).

Use case: Sometimes requested materials are delivered to a "self-service-area" where the patrons can pick them up and check them out themselves. For privacy reasons/data protection we are only printing the patron´s barcode on the slip, not the name.

Scenarios:

1. Scenario
   • Given create and edit mode for Staff slips (Settings > Circulation > Staff Slips)
   • When the curly braces are clicked in the rich text editor
   • Then Requester barcode should be an available token
2. Scenario
   • Given a staff slip (e.g. Hold or Transit) is displaying in preview mode in Settings CB: We decided by slack on Dec 5th that we didn't need this token in the transit slip and I failed to update this story accordingly.
   • When the Requester barcode token has been added
   • Then a realistic looking user barcode should display as an example in preview (not sure how preview works - does it pull from real data?)
3. Scenario
   • Given a staff slip (e.g. Hold or Transit) contains the Requester barcode token
   • When the staff slip is previewed in the printer dialogue and/or printed
   • Then the Requester barcode token should be replaced with the user barcode for the requester in question