feat(api-server): add insertPosition for addSongToQueue

[franz-dc]

Closes #2803, but hooking into POST /api/v1/queue instead of creating a new endpoint.

Request body:

{
  "videoId": "...",
  "insertPosition": "INSERT_AFTER_CURRENT_VIDEO"
}

insertPosition can be omitted and will default to the original behavior (INSERT_AT_END).

[cireCloud]

Hello. Would it be possible to have index as well? So it can be removed later on.
Or at least response to give index it was placed in? Thanks!