screenshots improvement

we also may consider whether GET /machines/:id/screenshots shouldn't return all available screenshots of that machine? btw. now it is automatically present in GET /machine/:id in an array screenshots but in dbv I would say that it is available nowhere

Start by locating the handlers for GET /machines/:id/screenshots and GET /machine/:id, then inspect how screenshots are represented in the database. Clarify whether the endpoint should return every available screenshot and how that relates to the screenshots array in the machine response; done requires an agreed response behavior and coverage for it.

Written by the indexing model from the issue text.