Bug 37380: Add get_control_number() to the metadata extractor

Bug 37380: Add get_control_number() to the metadata extractor

This simple patch implements C4::Biblio::GetMarcControlnumber in the
right spot on the Koha::* namespace.

To test:
1. Apply this patches
2. Run:
   $ ktd --shell
  k$ prove t/db_dependent/Koha/Biblio/Metadata/Extractor/MARC.t
=> SUCCESS: Tests pass!
3. Sign off :-D

Signed-off-by: Sam Lau <samalau@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>