docs: add info about custom errors via APIError to hooks overview (#13047)

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### What?

I was searching for info on how to return custom errors in hooks and
only came upon this discord answer by Dan Ribbons:

https://payloadcms.com/community-help/github/customize-rest-api-response-in-collection-hooks

### Why?

I think this info should be in the docs.

### How?

This PR adds a `Cusom Error Messages` section to the hooks-overview
page, detailing the usage of `APIError` as proposed by Dan Ribbons in
the above discord answer.

Co-authored-by: Paul Popus <paul@payloadcms.com>

Author: codeflorist

docs/hooks/overview.mdx

@@ -127,6 +127,22 @@ const afterChange = ({ doc }) => {
 
 Hooks are only triggered on the server and are automatically excluded from the client-side bundle. This means that you can safely use sensitive business logic in your Hooks without worrying about exposing it to the client.
 
+## Custom Error Messages
+
+You might want to return custom error messages in the API or admin panel in your hooks, if an operation cannot be performed - e.g. if a rate limit was exceeded. For this you can leverage the `APIError` class like this:
+
+```ts
+import { APIError, type CollectionBeforeChangeHook } from 'payload'
+
+const beforeChangeHook: CollectionBeforeChangeHook = async ({ data }) => {
+  ...
+  if (rateLimitExceeded) {
+     throw new APIError('You have sent too many requests', 429)
+  }
+  return data
+}
+```
+
 ## Performance
 
 Hooks are a powerful way to customize the behavior of your APIs, but some hooks are run very often and can add significant overhead to your requests if not optimized.