rtmp-services: Update Facebook Live encoder settings
As commented on: https://github.com/jp9000/obs-studio/commit/cab28190337255a85bbc7b244f2821f3adebeb5f#commitcomment-17482672
And according to: https://www.facebook.com/facebookmedia/get-started/live
Max 2-second keyframe interval and max video bitrate of 2500.
Closes jp9000/obs-studio#541