Add inference doc code examples

[iuliaferoli]

I'm adding inference doc code examples per #2429

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[pquentin]

Thanks Iulia! Note that simply adding the pages is not enough, you also have to run python utils/generate-examples.py after having cloned the client-flights-recorder repository. And then check that the results make sense. I'm happy to assist more.

[iuliaferoli]

Hey Quentin!
I've generated the examples and fixed a few minor details.
For example, it generated inference_id instead of model_id; so I think this also needs to be changed in the docs here: https://elasticsearch-py.readthedocs.io/en/latest/api/inference.html

Also I've had some trouble with the branches so it looks quite messy - still trying to get rid of having the client changes in here as well instead of in the separate PR.

[iuliaferoli]

@pquentin I updated these examples with inference_id instead of model_id