Adds transaction with watched key example script. (#2297)

* transction example improved

* readme fixed

* delay added for watched key changes

* pooling error fixed on recursion

* Minor comment update.

Co-authored-by: Ajay <ajay.markana@yudiz.com>
Co-authored-by: Simon Prickett <simon@redis.com>

Closes #2280.

examples/transaction-with-watch.js

@@ -0,0 +1,40 @@
+import { createClient, WatchError } from 'redis';
+
+const delay = (ms) => new Promise((resolve) => setTimeout(resolve, ms));
+const client = createClient();
+await client.connect();
+
+function restrictFunctionCalls(fn, maxCalls) {
+  let count = 1;
+  return function (...args) {
+    return count++ < maxCalls ? fn(...args) : false;
+  };
+}
+
+const fn = restrictFunctionCalls(transaction, 4);
+
+async function transaction() {
+  try {
+    await client.executeIsolated(async (isolatedClient) => {
+      await isolatedClient.watch('paymentId:1259');
+      const multi = isolatedClient
+        .multi()
+        .set('paymentId:1259', 'Payment Successfully Completed!')
+        .set('paymentId:1260', 'Refund Processed Successfully!');
+      await delay(5000); // Do some changes to the watched key during this time...
+      await multi.exec();
+      console.log('Transaction completed Successfully!');
+      client.quit();
+    });
+  } catch (error) {
+    if (error instanceof WatchError) {
+      console.log('Transaction Failed Due To Concurrent Modification!');
+      fn();
+    } else {
+      console.log(`Error: ${error}`);
+      client.quit();
+    }
+  }
+}
+
+transaction();