Bug 23667: Add route to GET /items

Bug 23667: Add route to GET /items

This patchset introduces a route to fetch items. It relies on the
already implemented code/mappings to get a single item.

To test:
- Apply this patches
- Run:
  $ kshell
 k$ prove t/db_dependent/api/v1/items.t
=> SUCCESS: Tests pass!
- Try the endpoint with your favourite API tool (Postman?)
- Sign off :-D

Note: to do exact searching on barcode, you need to build the query like
this:

GET /api/v1/items?external_id=<your_barcode>&_match=exact

Signed-off-by: Jesse Maseto <jesse@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>