Some improvements on how to use the contact roles

Issue #88 (closed)

This MR fixes some of the urls & introduces minor changes on the schemas, so that we can query the contact roles as:

GET /backend/api/v1/devices/{deviceId}/device-contact-roles?include=contact

(I needed those fixes in order to make the frontend integration in https://gitlab.hzdr.de/hub-terra/sms/frontend/-/merge_requests/229)