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.
"of type" matches the ticket but since we've changed the values it might not be best any more. "41 alerts of type Drugs" reads a bit oddly. What about "41 alerts for Drugs"?

This isn't a blocker to merging since we can always come back and tidy this up next week when @AliceNewton is around