[nrk] Add chapter and login support

[MrDemocracy]

IMPORTANT: PRs without the template will be CLOSED

Description of your pull request and other information

Adds support for downloading in the EU using the --username and --password (optional) parameters. Also implemented chapters extraction. It extracts the "intro end" and "skip credits" markers too. Additionally, the timestamp now uses the oldest value from either "publication date", "available from" or the previously used "timestamp" value.

Finally, cleaned up the code slightly by removing a seemingly unnecessary function and changed the extractor to no longer skip encrypted streams as unencrypted streams are not always available. These final changes seem to have fixed the two other open issues for this extractor.

Fixes

• NRK error 400 when downloading manifest JSON #3271
• Adding username/password support for tv.nrk.no #2513
• [Broken] NRK: live tv extractor does not work #1304

Template

Before submitting a pull request make sure you have:

• At least skimmed through contributing guidelines including yt-dlp coding conventions
• Searched the bugtracker for similar pull requests

In order to be accepted and merged into yt-dlp each piece of code must be in public domain or released under Unlicense. Check all of the following options that apply:

• I am the original author of this code and I am willing to release it under Unlicense
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• Fix or improvement to an extractor (Make sure to add/update tests)
• New extractor (Piracy websites will not be accepted)
• Core bug fix/improvement
• New feature (It is strongly recommended to open an issue first)