add defineConfig utility

this change adds a new `defineConfig` utility that developers can use in their `open-next.config.ts`
file to easily generate a configuration compatible with the adapter

Author: dario-piotrowicz

examples/playground14/open-next.config.ts

@@ -1,26 +1,6 @@
-import type { OpenNextConfig } from "@opennextjs/aws/types/open-next.js";
 import cache from "@opennextjs/cloudflare/kv-cache";
+import { defineConfig } from "@opennextjs/cloudflare/config";
 
-const config: OpenNextConfig = {
-  default: {
-    override: {
-      wrapper: "cloudflare-node",
-      converter: "edge",
-      incrementalCache: async () => cache,
-      queue: "direct",
-      // Unused implementation
-      tagCache: "dummy",
-    },
-  },
-
-  middleware: {
-    external: true,
-    override: {
-      wrapper: "cloudflare-edge",
-      converter: "edge",
-      proxyExternalRequest: "fetch",
-    },
-  },
-};
-
-export default config;
+export default defineConfig({
+  incrementalCache: cache,
+});