Task/581 v1 context entities attributes 4ops

### Description
Four new conv ops:
GET/PUT/POST/DELETE /v1/contextEntities/type/TYPE/id/ID/attributes/ATTR_NAME

Fixed in https://github.com/telefonicaid/fiware-orion/commit/2b27661da14fc7f8d2b9c1fc84fc8b99dfb52887