apacheHttpd: add link to acme nixos test

pkgs/servers/http/apache-httpd/2.4.nix

···
 { lib, stdenv, fetchurl, perl, zlib, apr, aprutil, pcre, libiconv, lynx
+, nixosTests
 , proxySupport ? true
 , sslSupport ? true, openssl
 , http2Support ? true, nghttp2
···
 
   passthru = {
     inherit apr aprutil sslSupport proxySupport ldapSupport luaSupport lua5;
+    tests = {
+      acme-integration = nixosTests.acme;
+    };
   };
 
   meta = with lib; {