Bug 27855: Make GET /patrons/:patron_id use objects.find

Bug 27855: Make GET /patrons/:patron_id use objects.find

This patch makes the route for fetching a patron use the objects.find
helper instead of a plain Koha::Patrons->find. This gives the controller
embedding superpowers.

To test, we just need to check nothing broke:
1. Apply this patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/api/v1/patrons.t
=> SUCCESS: Tests pass!
3. Sign off :-D

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>