docs: adds onInit to payload config options (#11069)

This PR adds the `onInit` function to the Payload config options table.

Author: akhrarovsaid

docs/configuration/overview.mdx

@@ -87,6 +87,7 @@ The following options are available:
 | **`upload`**               | Base Payload upload configuration. [More details](../upload/overview#payload-wide-upload-options).                                                                                                                           |
 | **`routes`**               | Control the routing structure that Payload binds itself to. [More details](../admin/overview#root-level-routes).                                                                                                             |
 | **`email`**                | Configure the Email Adapter for Payload to use. [More details](../email/overview).                                                                                                                                           |
+| **`onInit`**               | A function that is called immediately following startup that receives the Payload instance as its only argument.                                                                                                             |
 | **`debug`**                | Enable to expose more detailed error information.                                                                                                                                                                            |
 | **`telemetry`**            | Disable Payload telemetry by passing `false`. [More details](#telemetry).                                                                                                                                                    |
 | **`rateLimit`**            | Control IP-based rate limiting for all Payload resources. Used to prevent DDoS attacks, etc. [More details](../production/preventing-abuse#rate-limiting-requests).                                                          |