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.  
That linked example is the result of a request to a valid resource but attempting to operate on an invalid user; hence, the request is invalid and 400 is appropriate. The expectation with a 400 error is that something about the request itself is bad; in this case, the request would be perfectly acceptable if the course state were different.