fix: update iframe feature policy

[a-asad]

Description

It's a fix for this issue. It's needed to fix the Xblock video play button not working on Chrome for youtube videos due to the iframe security policy. Chrome blocks playing a youtube video programmatically when the iframe is not inside the parent window, which in our case is inside the Xblock iframe.

Testing Instructions

• Check out master/main
• Add a YouTube video to a course unit
• Preview the course in Chrome(or any Chromium-based browser)
• Navigate to the respective video section and play the video using the video player's play button. The video will not play.

Now check out this PR.

• Refresh the page and play the video again.
• It should start playing this time.

[openedx-webhooks]

Thanks for the pull request, @a-asad!

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[bradenmacdonald]

@a-asad Thanks! Please get your CLA in place and let us know when this is ready for review. I'll have to ask the Security Working Group to take a look as they need to review any changes to this policy.