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.
Let's drop the `and` from the value, as per https://github.com/alphagov/finder-api/pull/46