[YouTube] Implement support for collaborators

[FineFindus]

Implements support for extracting the collaborators of a video. This allows client apps to display them, if they wish so. The first collaborator is equivalent to the creator/uploader of the video.

Ref: #1397

• I carefully read the contribution guidelines and agree to them.
• I have tested the API against NewPipe.
• I agree to create a pull request for NewPipe as soon as possible to make it compatible with the changed API.

[FineFindus]

There's currently naturally a lot of duplicate code between extracting all the collaborators details, and extracting just a single detail (e.g. the URL). Maybe it would be better to extract them into separate functions? Or maybe it would be even better deprecated the singular uploader methods and always return at least one creator? That may have a small performance cost, though in our use-case we are always accessing all of them.

[absurdlylongusername]

There's currently naturally a lot of duplicate code between extracting all the collaborators details, and extracting just a single detail (e.g. the URL). Maybe it would be better to extract them into separate functions? Or maybe it would be even better deprecated the singular uploader methods and always return at least one creator? That may have a small performance cost, though in our use-case we are always accessing all of them.

#1360 (comment) perhaps related