HTTPS for YouTube iframe src

[jonkafton]

What are the relevant tickets?

N/A

Description (What does it do?)

Fixes an issue where we try to load YouTube videos over HTTP in a page loaded over TLS causing the video not to display and error e.g.

Mixed Content: The page at 'https://rc.learn.mit.edu/?resource=17315' was loaded over HTTPS, 
but requested an insecure frame 'http://www.youtube.com/embed/BYM_Bko4Tnc'. 
This request has been blocked; the content must be served over HTTPS.

How can this be tested?

On RC, videos should display correctly in the learning resource drawer (it's impractical to serve on HTTPS locally - we have yarn dev --experimental-https but would also need backend to do same):

Additional Context