Add schema for drug device alerts

We should check that we want to actually use single-select here. After a discussion with @alicebartlett we decided single select currently requires no modification to go live (as multi select will require work to not collapse when using only 2 options) although we should consider the impact of using single selects on our finder endpoints.
'for' seems to make more sense for now. Let's use that and change later if we need to.