earthly: init module (#6265)

Earthly is a build configuration framework utilizing buildkit and
Dockerfile-like syntax for simplicity and fast builds.

modules/programs/earthly.nix

@@ -0,0 +1,40 @@
+{ config, lib, pkgs, ... }:
+
+let
+
+  cfg = config.programs.earthly;
+
+  yamlFormat = pkgs.formats.yaml { };
+
+in {
+  meta.maintainers = [ lib.hm.maintainers.folliehiyuki ];
+
+  options.programs.earthly = {
+    enable = lib.mkEnableOption "earthly";
+
+    package = lib.mkPackageOption pkgs "earthly" { };
+
+    settings = lib.mkOption {
+      type = yamlFormat.type;
+      default = { };
+      description = ''
+        Configuration written to ~/.earthly/config.yml file.
+        See https://docs.earthly.dev/docs/earthly-config for supported values.
+      '';
+      example = lib.literalExpression ''
+        global = {
+          disable_analytics = true;
+          disable_log_sharing = true;
+        };
+      '';
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    home.packages = [ cfg.package ];
+
+    home.file.".earthly/config.yml" = lib.mkIf (cfg.settings != { }) {
+      source = yamlFormat.generate "earthly-config" cfg.settings;
+    };
+  };
+}