Bug 30165: Make q parameter 'multi'

Bug 30165: Make q parameter 'multi'

This patch changes the q_param definition so the defined query parameter
is repeatable. This way JSON::Validator will always generate an arrayref
for it and won't skip occurences.

The objects.search helper is updated to always consider the 'q'
parameter as an array, as expected.

To test:
1. Apply the regression tests patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/api/v1/query.t
=> FAIL: Tests fail!
3. Apply this patch
4. Repeat 2
=> SUCCESS: Tests pass!
5. Sign off :-D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>