treewide: pkgs.pkgconfig -> pkgs.pkg-config, move pkgconfig to alias.nix

continuation of #109595

pkgconfig was aliased in 2018, however, it remained in
all-packages.nix due to its wide usage. This cleans
up the remaining references to pkgs.pkgsconfig and
moves the entry to aliases.nix.

python3Packages.pkgconfig remained unchanged because
it's the canonical name of the upstream package
on pypi.

pkgs/development/libraries/p11-kit/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchFromGitHub, fetchpatch, autoreconfHook, pkgconfig, which
+{ stdenv, fetchFromGitHub, fetchpatch, autoreconfHook, pkg-config, which
 , gettext, libffi, libiconv, libtasn1
 }:
 
@@ -21,7 +21,7 @@ stdenv.mkDerivation rec {
   # at the same time, libtasn1 in buildInputs provides the libasn1 library
   # to link against for the target platform.
   # hence, libtasn1 is required in both native and build inputs.
-  nativeBuildInputs = [ autoreconfHook pkgconfig which libtasn1 ];
+  nativeBuildInputs = [ autoreconfHook pkg-config which libtasn1 ];
   buildInputs = [ gettext libffi libiconv libtasn1 ];
 
   autoreconfPhase = ''