agenix-rekey: move to flake part

nix/agenix-rekey.nix

@@ -0,0 +1,29 @@
+{
+  inputs,
+  ...
+}:
+{
+  imports = [
+    inputs.agenix-rekey.flakeModule
+  ];
+
+  perSystem =
+    { config, ... }:
+    {
+      agenix-rekey.nixosConfigurations = inputs.self.nixosConfigurations;
+      devshells.default = {
+        commands = [
+          {
+            inherit (config.agenix-rekey) package;
+            help = "Edit, generate, and rekey secrets";
+          }
+        ];
+        env = [
+          {
+            name = "AGENIX_REKEY_ADD_TO_GIT";
+            value = "true";
+          }
+        ];
+      };
+    };
+}