Add support for generative openai module

[dirkkul]

Using the generative module is currently possible, but he UX is not that great. Its usage could be improved by adding a explicit support for this kind of query:

Note:

• The module generative-openai needs to be enabled using ENABLE_MODULES=generative-openai
• You need an openai API key:OPENAI_APIKEY=some_key
• The tests should be skipped if no openai key is available
  For inspiration, check the python or go imlpementation

[dirkkul]

Closed by #187