Fix File Q&A build error due to removed way of assigning options to the Formidable instance (#372)

* Pass maxFileSize attribute when instantiating IncomingForm()

Assigning a value through `form.maxFileSize` directly no longer works and will result in `Type error: Property 'maxFileSize' does not exist on type 'IncomingForm'.`

* Refactor Formidable instantiation acdg. to example shown in docs

Example usage acdg. to docs: e5e25d2fd9/README.md (formidable--incomingform)

apps/file-q-and-a/nextjs/src/pages/api/process-file.ts

@@ -26,8 +26,10 @@ export default async function handler(
   }
 
   // Create a formidable instance to parse the request as a multipart form
-  const form = new formidable.IncomingForm();
-  form.maxFileSize = 30 * 1024 * 1024; // Set the max file size to 30MB
+  const options = {
+    maxFileSize: 30 * 1024 * 1024 // Set the max file size to 30MB
+  }; 
+  const form = formidable(options);
 
   try {
     const { fields, files } = await new Promise<{