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/geis/default.nix

@@ -1,5 +1,5 @@
 { stdenv, fetchurl
-, pkgconfig
+, pkg-config
 , python3Packages
 , wrapGAppsHook
 , atk
@@ -36,7 +36,7 @@ stdenv.mkDerivation rec {
   pythonPath = with python3Packages;
     [ pygobject3  ];
 
-  nativeBuildInputs = [ pkgconfig wrapGAppsHook python3Packages.wrapPython];
+  nativeBuildInputs = [ pkg-config wrapGAppsHook python3Packages.wrapPython];
   buildInputs = [ atk dbus evemu frame gdk-pixbuf gobject-introspection grail
     gtk3 libX11 libXext libXi libXtst pango python3Packages.python xorgserver
   ];