test(esl-media): e2e testing

[fshovchko]

Closes: #2709

@ala-n, do we need any other functionality tested or basic check for video/iframe tag is enough?

[ala-n]

Nope, checking the existence of an iframe is not enough.
From what I could suggest based on YouTube provider work we need:

1. Check that YouTube API is loaded, check that it is loaded once
2. We need to check the inner iframe is, actually, a YouTube and that it at least contains an ID of the required video
3. We need to check initial attributes as well (playsinline, autoplay, mute)
4. Ideally we need as much as possible including the ability to play etc. but unfortunately, YouTube no longer allows playing videos for unauthorized users (autotests including).

[codeclimate]

Code Climate has analyzed commit 1f1dc61 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 65.3% (0.0% change).

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