Add the tags of a vendor to the response of single vendor fetch (BE)

[MariusJulius]

Previous fix task: https://github.com/keeleinstituut/tv-tolkevarav/issues/474 Relates to: https://github.com/keeleinstituut/tv-tolkevarav/issues/460 , FE should work, after tags are returned from BE

To-do:

• add the tags of a vendor to the response of single vendor fetch as well (they seem to be added when fetching list) endpoint: GET https://api.dev.tolkevarav.eki.ee/translation-order/api/vendors/

[MariusJulius]

Marking as done as FE ticket was working: https://github.com/keeleinstituut/tv-tolkevarav/issues/460