Fetch linked channels

Checklist

• I am aware that this issue is being opened for the NewPipe Extractor, NOT the app, and my feature request will be dismissed otherwise.
• I made sure that there are no existing issues - open or closed - which I could contribute my information to.
• I have taken the time to fill in all the required details. I understand that the feature request will be dismissed otherwise.
• This issue contains only one feature request.
• I have read and understood the contribution guidelines.

Feature description

Some channels (eg, LTT) add references to other channels, usually others they operate, on the home tab of their channel. It doesn't seem currently possible to fetch these linked channels using NewPipeExtractor.

Why do you want this feature?

I'm an end user of LibreTube. I opened an issue on their repo first, and the dev referred me to here since the extractor doesn't support fetching this data.

I'd like the feature because it would make onboarding in YouTube third-party clients easier overall, when the user needs to quickly add the channels he wants to subscribe to.

Additional information

No response

Start by examining the existing YouTube channel extraction flow and the data returned for the LTT channel example. Determine where linked channels would be represented and how similar channel sections are fetched. Done means the extractor exposes the linked channels reliably, with coverage for the reported example and appropriate tests.