refator: put all modules under modules directory

modules/k8s/lib.nix

@@ -0,0 +1,35 @@
+{ lib, ... }:
+
+with lib;
+
+let
+  k8s = {
+    mkSecretOption = {description ? "", default ? null}: mkOption {
+      inherit description;
+      type = types.nullOr (types.submodule {
+        options = {
+          name = mkOption {
+            description = "Name of the secret where secret is stored";
+            type = types.str;
+          };
+
+          key = mkOption {
+            description = "Name of the key where secret is stored";
+            type = types.str;
+          };
+        };
+
+        config = mkDefault (if default == null then {} else default);
+      });
+      default = {};
+    };
+
+    secretToEnv = value: {
+      valueFrom.secretKeyRef = {
+        inherit (value) name key;
+      };
+    };
+  };
+in {
+  _module.args.k8s = k8s;
+}