Added oembed endpoint for pictures and video

Closes #1854 (closed)

Depends on front!1318 (merged)

Image example:

https://feat-oembed-front-4091.minds.io/api/v3/oembed?url=https%3A%2F%2Ffeat-oembed-front-4091.minds.io%2Fnewsfeed%2F1263811756283662340

Videos and feeds don't seem to be working on sandbox so unable to test anywhere other than local