Transactional example

[erikvanoosten]

An example on how to use the transactional producer.

This example was not tested, a thorough review by the authors is highly appreciated.

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[erikvanoosten]

Sorry, I will redo this PR with the correct credentials...

[guizmaii]

@erikvanoosten Did you remake this PR? Did we merge it? 🤔

[erikvanoosten]

This is the remake: #440.
However, #440 was totally broken and closed without merging.
Much later, I created #644 (a transactional test) which has been merged.
In short: there is no documentation for using transactional yet, but at least there is a test that can be used as example.

[guizmaii]

Thanks for these tests! Super valuable contribution! 🙏 ❤️