Add field on line item batch updater to add parts

[Tiffany Little]

Although there's already a bug around being able to add parts during an acq upload (see bug 1203866) we also need the ability to add parts while working in a PO.

At first I was thinking of adding this to the PO-level batch updater, but I think it's more appropriate on the line item level batch updater. We already have a field for Call Number, so I think this fits there.

If the line item is linked to a bib record already, I'd like to see a combobox populated by non-deleted parts already existing on the record so that you can choose from a list. Similar to some other fields in Angular Acq (like the selection list combobox on Load MARC Order Records), you should also be able to create a part label on the fly that would be created on the associated eg_bib_id.

This is becoming problematic for us at PINES because often acq on-order copies are being created on series records (which is otherwise fine), but with no part patrons aren't able to place on-order holds on them. It would also be really useful when cataloging to already have the part applied to further distinguish which temp acq barcode goes to which volume.