DEICH-5521 make it possible to close ILL
This commits does two things:
- Add parameter 'closed' to ill/availability endpoint which will make it always return 0 items for num_available_library. Hopefully this would make all requests from bibsok fail.
- Deny adding ILL any requests by placing holds on deichman.no if branch ILL (Fjernlån) is closed (if branchnotes = "BRANCH_CLOSED")
Closes DEICH-5521