Git: Split git home-manager config into user-specific and machine-user specific parts

modules/hosts/tux/users/weckyy702/git.nix

@@ -0,0 +1,5 @@
+{
+  flake.modules.homeManager.tux-weckyy702-git = {
+    programs.git.signing.key = "/home/weckyy702/.ssh/id_ed25519_github_sign";
+  };
+}

modules/hosts/tux/users/weckyy702/weckyy702.nix

@@ -18,6 +18,8 @@
           blueman-applet
           prusa-slicer
           backlight
+
+          tux-weckyy702-git
         ];
     };
   };