Consider standardizing 7-day max-age cap for cookies set via JavaScript

[arichiv]

Two browsers are already doing this (Safari and Brave). It might be worth documenting in the standard.

[annevk]

cc @johannhof @johnwilander @bvandersloot-mozilla

[johannhof]

Given that two other browsers are explicitly deciding against this I'd be okay with providing the spec with a standardized means to do this but leaving the decision up to the implementer :)