Refactor and add generators for keystatic and package

The changes include refactoring the create-reader in cms keystatic and changing @keystatic/next version. Additionally, code generators for keystatic and package have been added, and corresponding templates have been organized into their respective directories.

packages/cms/keystatic/src/keystatic-route-handler.ts

@@ -0,0 +1,7 @@
+import { makeRouteHandler } from '@keystatic/next/route-handler';
+
+import config from './keystatic.config';
+
+export const keystaticRouteHandlers = makeRouteHandler({
+  config,
+});