title: How to write custom endpoints with parameters not related to any specific entity
body: <p>I'm trying to write custom GET endpoints, which must have one or more custom parameters, but not built on top of specific entity.</p>
  
  <p>Something like:
  /assets/{device_id}/{scene_id}/{maybe_other_param}</p>
  
  <p>which I imagine to be just own controller class, in which I do something, calculate values from input, read some data manually and return array of entities.
  What I only get is an Asset entity, but it requires {device} and {scene} to be properties of this entity...</p>
  
  <p>I don't want this to work as exposed entity with filter by its properties, I just need simple endpoint seen in API, as normal custom controller which takes some params, do stuff and return json.</p>
  
  <p>It sounds like simple thing, but I read tons of documentation and examples and still didn't find anything. Is this even possible in API-platform?</p>