Bug 24461: Add to_api_mapping to Koha::Acquisition::BasketGroup

Bug 24461: Add to_api_mapping to Koha::Acquisition::BasketGroup

This patch adds to_api_mapping to the Koha::Acquistion::BasketGroup
class.

To test:
1. Compare the mapping with the one on the RFC
=> SUCCESS: They match
2. Sigh 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: Martin Renvoize <martin.renvoize@ptfs-europe.com>