move nixlang impls to their own directory tree

modules/dynamic-overrides.nix

@@ -0,0 +1,21 @@
+# Managed by dynix.
+{ lib, ... }:
+
+lib.mkMerge [
+  {
+    services.gotosocial = {
+      enable = true;
+      setupPostgresqlDB = true;
+      settings = {
+        application-name = "example!";
+        host = "yuki.local";
+      };
+    };
+  }
+  {
+    services.gotosocial.settings.application-name = lib.mkOverride 99 "removed herobrine";
+  }
+  {
+    services.gotosocial.settings.application-name = lib.mkOverride 98 "reädded herobrine";
+  }
+]