Hide watched videos in what's new feed

[phly95]

Checklist

• I checked, but didn't find any duplicates (open OR closed) of this issue in the repo.
• I have read the contribution guidelines given at https://github.com/TeamNewPipe/NewPipe/blob/HEAD/.github/CONTRIBUTING.md.
• This issue contains only one feature request. I will open one issue for every feature I want to request.

Describe the feature you want

In the subscription feed/what's new, it would be handy to allow hiding of watched videos (and manually marking as watched) as well as having a max time threshold (eg. No videos older than 1 week) to keep the subscription feed clean.

Is your feature request related to a problem? Please describe it

Seeing videos you've already watched in a subscription feed makes the feed feel like there's more stuff than there is. It's like an itch you can't scratch.

Additional context

How will you/everyone benefit from this feature?

This will allow users to reach the YouTube equivalent of Inbox zero for subscriptions.

[triallax]

Fixed by #3371.