Bug 28272: Add unseen_renewals for checkouts

Bug 28272: Add unseen_renewals for checkouts

 t/db_dependent/api/v1/checkouts.t ...................... 7/93
 #   Failed test '200 OK'
 #   at t/db_dependent/api/v1/checkouts.t line 198.
 #          got: '500'
 #     expected: '200'

 #   Failed test 'exact match for JSON Pointer ""'
 #   at t/db_dependent/api/v1/checkouts.t line 198.
 #     Structures begin differing at:
 #          $got->{unseen_renewals} = Does not exist
 #     $expected->{unseen_renewals} = '0'
 t/db_dependent/api/v1/checkouts.t ...................... 88/93
 #   Failed test '200 OK'
 #   at t/db_dependent/api/v1/checkouts.t line 218.
 #          got: '500'
 #     expected: '200'

 #   Failed test 'exact match for JSON Pointer ""'
 #   at t/db_dependent/api/v1/checkouts.t line 218.
 #     Structures begin differing at:
 #          $got->{max_renewals} = Does not exist
 #     $expected->{max_renewals} = '1'
 # Looks like you failed 4 tests of 93.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>