Bug 23156: [18.11] Add pagination to checkouts in ILS-DI GetPatronInfo service

Bug 23156: [18.11] Add pagination to checkouts in ILS-DI GetPatronInfo service

When patrons have a lot of checkouts, GetPatronInfo can take a lot of
time. This patch introduces two new parameters to allow pagination of
this list of checkouts

Also, fix a warning in C4::ILSDI::Services::GetPatronInfo

Test plan:
1. Go to /cgi-bin/koha/ilsdi.pl?service=GetPatronInfo&patron_id=X&show_loans=1
   where X is a borrowernumber of a patron who has several checkouts
   Verify that all checkouts are listed
2. Add '&loans_per_page=1&loans_page=1' to the URL. Verify that you have
   now only one checkout listed, and that there is a new element
   <total_loans> which contain the total number of checkouts
3. Increase the page number in the URL until you have seen all checkouts
4. prove t/db_dependent/ILSDI_Services.t

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>