feat(Collaborators): Add `Author#collaborators` and `Playlist#getCollaborators()` (#1203)

- Add `get collaborators()` inside `Author` class to add support for collaborators in search page data.
- Add `getCollaborators()` inside `Playlist` class to add support for collaborative playlists (example: https://www.youtube.com/playlist?list=PLaen7aJT3lIFptMwtTJkOvQtcxyKqQwlP). Requires authentication.

This does not work in channel (example: https://www.youtube.com/@KSI/videos) or playlist (example: https://www.youtube.com/playlist?list=PL6_iWvoCGAJlJUy9KFfGX9e41ZHB37wGX) because YouTube does not provide this data.
Video page already supports getting collaborators through `LockupView` fields.

Playlists themselves can also be collaborative (example: https://www.youtube.com/playlist?list=PLaen7aJT3lIFptMwtTJkOvQtcxyKqQwlP), but it requires an extra API call, and it is not accessible without being authenticated.

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Co-authored-by: LuanRT <luan.lrt4@gmail.com>