Bug 30212: Make Select2 available for ILL backends

Bug 30212: Make Select2 available for ILL backends

This patch makes select2 available for ILL backend developers to use on
their templates.

To test:
1. Have a configured backed and an ILL request
2. Open the inspector and load any action on the backend (intranet)
=> FAIL: no select2 asset is transfered from Koha to the browser
3. Apply this patch
4. Reload
=> SUCCESS: There's select2
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: Fridolin Somers <fridolin.somers@biblibre.com>