Task/581 v1 context entities attributes value 4ops

### DEscription
New set of convops:
GET/PUT/POST/DELETE /v1/contextEntities/type/{type}/id/{id}/attributes/{attr_name}/{id_value}

The code is copied from an earlier serviceRoutine, also DELETE (it's 'brother' service'), so, there we have it, at least.
Can't respond to if it is implemented everywhere it should be (I doubt it).
Let's create an issue for it?