Course teams can turn off Chinese Caching from studio (BLD-1207)

Allow turning off Chinese CDN from Studio.
**Issue**: [BLD-1207](https://openedx.atlassian.net/browse/BLD-1207)

Please review: @tymofij 
Will this show in the Studio Advanced Settings?

Do we have anyone to review this documentation? It seems odd to say that "currently it only makes a difference for China". 

@lamagnifica Alison, would you be the right person to work on the wording?