Add the ability to add Gift preparations with a quantity of 0

[lexiclevenger]

Is your feature request related to a problem? Please describe.

Hi Grant Fitzsimmons, quick question about giftpreparations - through the workbench I'm able to add a prep with a quantity of 0 to a gift, which is excellent because we have a case with the Herbarium where they clone a sheet to send to another institution, and I don't want them to increase the preparation count just to lower it straight away. However I just want to check that this isn't seen as a bug and this option will disappear!

In addition, it would actually be great to be able to do the same thing from the UI i.e. add preps with a count of 0. Right now if you try to do that it unticks the prep so it won't get added to the gift.

Describe the solution you'd like
Give users the option to enable adding preparations with a quantity of 0 to interactions using the Preparations dialog. If possible, it may be best to add this as an option at the collection level to suit the preferences and workflows used in each collection.

Reported by Dan Baker @ CSIRO (Asana)