[telequebec] Support coucou subdomain URLs

[waptaff]

The zonevideo.telequebec.tv code works on coucou.telequebec.tv, so just
ensure those coucou URLs are recognized.

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• At least skimmed through adding new extractor tutorial and youtube-dl coding conventions sections
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[dstftw]

Don't capture groups you don't use. Read coding conventions. Add tests.

[Thieum]

Would it work with squat too? see #18503

[waptaff]

Would it work with squat too? see #18503

Unfortunately no, more code changes will be needed for squat :(

[waptaff]

Don't capture groups you don't use. Read coding conventions. Add tests.

Done. Please re-evaluate this pull request.

Thanks,