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 
"Enter true or false. If true, HTML5 videos are cached."
Does this leave out anything that should be stated? 
I didn't see any mention of CDN in the JIRA ticket, and agree with @cahrens that mentioning a single use case (China) is too specific.