Add GitLab and GitLab Runner.

Change-Id: Iaf9bbf4567db2ee7c5b36c6be767825093a2881d
diff --git a/images.nix b/images.nix
index cc6f495..137b4e8 100644
--- a/images.nix
+++ b/images.nix
@@ -54,6 +54,8 @@
 
   mailcow = pkgs.callPackage ./mailcow/default.nix { };
 
+  gitlab-runner = pkgs.callPackage ./gitlab-system/gitlab-runner/default.nix { };
+
   nextcloud = img {
     name = "docker.benkard.de/mulk/nextcloud";
     contents =