Store video files on external platform

[jo-elimu]

Description

Video files are too large to be stored directly in the database, so refactor the software to fetch videos from an external URL instead.

• [x] https://github.com/elimu-ai/webapp/issues/1945
• [ ] https://github.com/elimu-ai/webapp/issues/1934
• [ ] https://github.com/elimu-ai/content-provider/issues/127
• [ ] https://github.com/elimu-ai/content-provider/issues/49

Why?

This is needed because the webapp crashes when there is a large collection of videos to be loaded from the database.