[Update] Approve "Performer Aspect Ratio"

[AdultSun]

Needs official approval: https://guidelines.stashdb.org/docs/performers/performer-images/#performer-aspect-ratio

I don't believe there's much controversy on 2:3 as the preferred ratio here, but instead we'll need to consider how rigid or lenient we'll want to be in enforcing it. The current phrasing is, "There is no hard requirement for enforcing this ratio at this time."