MA-104 Studio backend for video_upload

https://openedx.atlassian.net/browse/MA-104
Advanced Setting for "Video Upload Pipeline".
Feature Flag for "ENABLE_VIDEO_UPLOAD_PIPELINE".
Use AssetMetaData store to persist video upload information.

@andy-armstrong @gwprice I have created this new PR to reflect only the initial backend studio support of our feature.  Please review again.  
@gwprice These were the states listed in the wiki document and I didn't hear any discussion on this at that time.  We do need to progress quickly on this feature and yes, we'll need to revisit it, if needed, as we integrate with VEDA and the UI.