FR: vi-movement keys for next/previous item of same kind

[Nemo157]

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

When doing interactive hunk selection I want to navigate across expanded hunks. It seems there are keybindings for that:

[Previous item of the same kind (page-up)]
[Next item of the same kind (page-down)]

but I don't have page-up/down keys on my keyboard.

Describe the solution you'd like

Some vi-movement-like keybindings for this navigation. My first thought was shift+k + shift+j.

Describe alternatives you've considered

Updating my keyboard layout to include page-up/down 😁

[yuja]

cc @arxanas