Building a custom integration - How to start?

I would really like to build a custom integration for Zammad with our document management system. Its a system not widly spread, so this is definitivly no feature request, but for a rather big open source project, I do find very little documentation on how to do custom development.

I see that there is the system β†’ packages menu, but the docs do not state how the structure of such a package must look like. I see there are integrations like GitHub in the latest version, but I did not find any templates how to build something on my own, yet.

Can anyone provide any details or starting points to this? I would be happy to put all the stuff I get to a public repo or into the official documentation to help others.

Zammad is a great tool, but the power of open source should be the ease of building our own solution on top of it…

Thanks for any help!