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/servers/asterisk/default.nix

@@ -2,7 +2,7 @@
   jansson, libedit, libxml2, libxslt, ncurses, openssl, sqlite,
   util-linux, dmidecode, libuuid, newt,
   lua, speex,
-  srtp, wget, curl, iksemel, pkgconfig
+  srtp, wget, curl, iksemel, pkg-config
 }:
 
 let
@@ -14,7 +14,7 @@ let
                     dmidecode libuuid newt
                     lua speex
                     srtp wget curl iksemel ];
-    nativeBuildInputs = [ util-linux pkgconfig ];
+    nativeBuildInputs = [ util-linux pkg-config ];
 
     patches = [
       # We want the Makefile to install the default /var skeleton