Add example of k6/experimental/fs module

examples/experimental/fs/bonjour.txt

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+Bonjour, tout le monde!

examples/experimental/fs/fs.js

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+import { open } from "k6/experimental/fs";
+
+export const options = {
+	vus: 100,
+	iterations: 1000,
+};
+
+// As k6 does not support asynchronous code in the init context, yet, we need to
+// use a top-level async function to be able to use the `await` keyword.
+let file;
+(async function () {
+	file = await open("bonjour.txt");
+})();
+
+export default async function () {
+	const fileinfo = await file.stat();
+	if (fileinfo.name != "bonjour.txt") {
+		throw new Error("Unexpected file name");
+	}
+}