Allow creating a submission with string or list of strings for packageName

[pkalita-lbl]

This is a bit of follow on work to the changes for #1367.

These changes allow a client to create a new submission using either a list of strings or single string for the packageName field. The reason for this comes down to the fact that the release cycle for the Field Notes app is decoupled from the nmdc-server release cycle (by necessity, due to app store review delays).

The app already knows how to deal with packageName values coming from the server that are either string or lists of strings. But when creating a new submission, the app doesn't know a priori whether the server will accept a single string or an array of strings for the packageName. We will release an update to the app to make it send an array of strings by default, but it will take a little bit of time to get that change into user devices. In the meantime the app will continue sending a single string packageName for new submissions, and these backend changes will help ease that transition period.

P.S. In the future I'd like to use the information from the /api/version endpoint to make decisions in the app about which features the server supports. Hopefully that will mean fewer backend changes like this in the future. But it'll take a bit of architectural work in the app to do that, and that sadly isn't the top priority at the moment.