flex config schema not shown in SwaggerDocs for POST /sensor/ID/schedule/trigger

[nhoening]

The triggering endpoint on the sensor API does not include schema details about flex-model and flex-config, see screenshot.

Compare to the same endoint on the asset, where you can browse both flex config schemas nicely.

We don't use the sensor one that much, actually thinking about deprecating it, so we should fix this one only if it is easy.

Originally posted by @nhoening in #1951 (review)

[Flix6x]

(In #1982 I tried fixing this, but it made tests fail. I do know what to do to resolve this issue, but because it is a bit more cumbersome to get it done I decided to keep it out of scope for #1982. I'm just having trouble unlinking that PR from this issue.)