feature request: newsletter api

[f321x]

Exposing basics of the Whatsmeow newsletter API would be greatly appreciated.

I already vibecoded this in my branch 9e8067e, createNewsletter seems to work, sendNewsletterMessage still segfaults, feel free to take these patches.

Thanks for maintaining these bindings.

[Labfox]

I've tried your patches, they don't seem to work for me. I'll debug it deeper soon.

[Labfox]

Okay, I've got a working copy. I'll create a branch and start adapting to the many refactoring that happened between your copy and the repository's current status