move git to own mod

nixosModules/git.nix

@@ -0,0 +1,24 @@
+{
+  lib,
+  config,
+  pkgs,
+  ...
+}:
+{
+  options.my.git.enable = lib.mkEnableOption "git with credential helper";
+
+  config = lib.mkIf config.my.git.enable {
+    environment.systemPackages = [ pkgs.git-credential-oauth ];
+
+    programs.git = {
+      enable = true;
+      config = {
+        init.defaultBranch = "main";
+        credential = {
+          helper = "oauth";
+          credentialStore = "cache";
+        };
+      };
+    };
+  };
+}