pkgconfig: rename to pkg-config (#55094)

Package attrs should map to the pname. It's confusing otherwise.

pkg-config is also the name used by most distributions:

Debian, Homebrew, Guix, OpenSuse

other distributions like FreeBSD ports, Fedora and Arch Linux call it
"pkgconf"

Waiting a few releases to make a tree-wide change to make it easier to
back-port things.