[idf1_extractor] Add new extractor (fulfilling support request #25671)

[bmensah]

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• At least skimmed through adding new extractor tutorial and youtube-dl coding conventions sections
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What is the purpose of your pull request?

• Bug fix
• Improvement
• New extractor
• New feature

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Description of your pull request and other information

In issue #25671 opened on June 15, a youtube-dl user requested that an extractor for videos from the site "idf1.fr" be added, with two example videos attached to the post. This pull request aims to resolve that issue.

[dstftw]

Have you even bothered to test it?

[bmensah]

Hi! my apologies; new to this. I thought that since all my unit tests passed, it was alright to go ahead and submit a pull request. I see now that even though the unit tests returned ok, trying to actually download the video still gives an error.