chore: update what-is-payload.mdx (#9942)

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### What?

update YouTube "What is Payload?" video

### Why?

Reflect 3.0 changes.

### How?

Fixes #

-->

Author: ncaminata

docs/getting-started/what-is-payload.mdx

@@ -7,8 +7,8 @@ keywords: documentation, getting started, guide, Content Management System, cms,
 ---
 
 <YouTube
-  id="In_lFhzmbME"
-  title="Payload Introduction - Closing the Gap Between Headless CMS and Application Frameworks"
+  id="ftohATkHBi0"
+  title="Introduction to Payload — The open-source Next.js backend"
 />
 
 **Payload is the Next.js fullstack framework.** Write a Payload Config and instantly get: