Add documentation / screenshots for the "Webhook ID" value

Problem/Motivation

The PayPal settings PayPal Checkout (Preferred) form has a "Webhook ID" field with the following description:

Required value when using Webhooks, used to verify the webhook signature.

But for users of the module it's unclear how to retrieve the value and when to use.
It would be great, if the field description could go a bit more into detail and perhaps the process could be shown here?:
https://www.drupal.org/node/3042053 →

That step by step documentation is super helpful!

Thank you!

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes