Home-manager: `home-manager news` should provide an option to only show "unread" news

[NobbZ]

Issue description

home-manager news prints a huge lists of "news", most of them are neither relevant for me, or I already read them.

Sometimes home-manager switch informs me about a given number of "unread and relevant news items".

Sadly those are not necessarily at the top of the paged output, but I have to sometimes find them somewhere in between.

Therefore it would be nice to have a way to only show unread news items.

[teto]

I vote for ditching news.nix altogether, its problematic on rebase, introduce some states, and duplicates git log effort.