maintainers: add redxtech

maintainers/maintainer-list.nix

···
     githubId = 816465;
     name = "Redvers Davies";
   };
+  redxtech = {
+    email = "[e-mail]";
+    github = "redxtech";
+    githubId = 18155001;
+    name = "Gabe Dunn";
+  };
   reedrw = {
     email = "[e-mail]";
     github = "reedrw";