Bug 28830: Add cni index for 003

Bug 28830: Add cni index for 003

This patch adds the cni/Control-number-identifier index to enable
searches to use the 003 field.

Test plan
1/ Apply patch
2/ Re-index using updated configurations
3/ Confirm cni:number searches yield the expected results
4/ Signoff

Split-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Pasi Kallinen <pasi.kallinen@koha-suomi.fi>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>