PgUp/PgDown in the "Files" view

[cherio]

Some of the commits have long lists of files. Scrolling through them in the Files view with just Up/Down is somewhat daunting. Same goes for Message view.

One good example of having long file lists and messages is when viewing commits left by etckeeper.

PgUp/PgDown keys seems to work well in some other views (e.g. Commit view). It would be very helpful to have the same in the Files & Message view. Honesty, having these keys work in any scrollable view would be great.

Version:
gitui --version
gitui nightly 2025-02-28 (99f6967)

[extrawurst]

#2496 should be a good reference for this

[savchenko]

Same for the "unstaged changes" view. Might be covered by the #2496 though (?)