Add git and gpg configs

Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>

users/common/configs/git/default.nix

@@ -1,6 +1,23 @@
+{ pkgs, ... }:
+
 {
   programs.git = {
     enable = true;
     lfs.enable = true;
+    signing = {
+      signByDefault = true;
+      key = null;
+    };
+    extraConfig.credential.helper = "store";
+    hooks = {
+      commit-msg = pkgs.writeScript "git-commit-msg" ''
+        #!${pkgs.runtimeShell}
+
+        git interpret-trailers --if-exists doNothing --trailer \
+          "Signed-off-by: $(git config user.name) <$(git config user.email)>" \
+          --in-place "$1"
+      '';
+    };
   };
 }
+