Bug 30880: Add 'branchonly' to OPACResultsUnavailableGroupingBy

Bug 30880: Add 'branchonly' to OPACResultsUnavailableGroupingBy

This patch adds a third option 'branch only' to the
OPACResultsUnavailableGroupBy system preference. This option will group
unavailable items by branch in the OPAC search results and NOT show
individual callnumbers or substatuses.

Note: This assumes OPACXSLTResultsDisplay is set to default.

To test:
1. Create a biblio record with 3 items with the following home branches:
Item A: Branch A
Item B: Branch A
Item C: Branch B
2. Check out Item A to yourself
3. Edit Item B to have a lost status
4. Go to Administration -> global system preferences. Search for
OPACResultsUnavailableGroupingBy.
5. By default, this preference will be set to 'branch'.
6. Open the OPAC in another tab, and search for your record.
7. Confirm the search results shows an Availability line with "Not
available: Branch A: Checked out (1). Branch A: Lost (1)." i.e. showing
both branch and substatus.
8. In your staff client tab, set OPACResultsUnavailableGroupingBy to
'substatus'.
9. Go back to your OPAC tab and search for your record. Confirm the
search results shows an Availability line with "Not available: Checked
out (1). Lost (1)." i.e. showing substatus only.
10. Apply patch, update database, restart services.
11. In your staff client tab, refresh the page. Confirm the options for
OPACResultsUnavailableGroupingBy have now changed to:
- branch and substatus
- substatus only
- branch only
12. Set OPACResultsUnavailableGroupingBy to 'branch only'.
13. Go back to your OPAC tab and search for your record. Confirm the
search results shows an Availability line with "Not available: Branch A
(2)." i.e. showing branch only.
14. Confirm the other two options still work as expected.

Sponsored-by: Chartered Accountants Australia and New Zealand
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>