home: git: extract 'delta' configuration

I want to be able to re-use it between different source control systems
(e.g: `jj`).

As a first step, extract it to a proper module so that I can have it
live in a single space.

modules/home/git/default.nix

@@ -42,34 +42,6 @@ in
 
     lfs.enable = true;
 
-    delta = {
-      enable = true;
-
-      options = {
-        features = "diff-highlight decorations";
-
-        # Less jarring style for `diff-highlight` emulation
-        diff-highlight = {
-          minus-style = "red";
-          minus-non-emph-style = "red";
-          minus-emph-style = "bold red 52";
-
-          plus-style = "green";
-          plus-non-emph-style = "green";
-          plus-emph-style = "bold green 22";
-
-          whitespace-error-style = "reverse red";
-        };
-
-        # Personal preference for easier reading
-        decorations = {
-          commit-style = "raw"; # Do not recolor meta information
-          keep-plus-minus-markers = true;
-          paging = "always";
-        };
-      };
-    };
-
     # There's more
     extraConfig = {
       # Makes it a bit more readable