[chelseafc] Add new extractor

[01001110]

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• You will be asked some questions, please read them carefully and answer honestly
• Put an x into all the boxes [ ] relevant to your pull request (like that [x])
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Before submitting a pull request make sure you have:

• Searched the bugtracker for similar pull requests
• Read adding new extractor tutorial
• Read youtube-dl coding conventions and adjusted the code to meet them
• Covered the code with tests (note that PRs without tests will be REJECTED)
• Checked the code with flake8

In order to be accepted and merged into youtube-dl each piece of code must be in public domain or released under Unlicense. Check one of the following options:

• I am the original author of this code and I am willing to release it under Unlicense
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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

Resolves #31412.

[dirkf]

Thanks for your work, even if I might have preferred qpr.co.uk!

I've made some suggestions. Try them out and I'll enable the CI test.

[Tom1380]

Anything new?

[aaron-tan]

I've tried to test this extractor by downloading the example URL video: https://www.chelseafc.com/en/video/first-half--manchester-united-v-chelsea--a--5smw5iate62dthdwoxsafx-csrrsy0%E2%80%A6 but unfortunately it returned HTTP Error 404: Forbidden. Is the extractor working?

[01001110]

I've tried to test this extractor by downloading the example URL video: https://www.chelseafc.com/en/video/first-half--manchester-united-v-chelsea--a--5smw5iate62dthdwoxsafx-csrrsy0%E2%80%A6 but unfortunately it returned HTTP Error 404: Forbidden. Is the extractor working?

@aaron-tan I just tested it with your URL, and it works fine.