Add quick start to generate access token in App Builder action

[purplecabbage]

Code can be taken from the example:

Generate access token in App Builder action

https://experienceleague.adobe.com/docs/experience-manager-learn/cloud-service/developing/extensibility/app-builder/jwt-auth.html?lang=en

Describe the solution you'd like
There are some minor code issues with that example that should be fixed at the same time