Custom Sobo Tutorial

[jduerholt]

This PR adds a notebook that shows how to setup sobo strategies with custom objective manipulations.

[LukasHebing]

A bit of information is missing for me to be able to understand the example:

• The parameters of f need to be explained: What will be passed as samples, callables, ...

def f(samples, callables, weights, X):
...

• The function for getting the index, should be explained a bit:

feature2index, _ = strategy.domain.inputs._get_transform_info(
    strategy.input_preprocessing_specs
)
feat_idx = feature2index["x_1"][0]

[jduerholt]

Thx, for the review. I will work on it ;)

[jduerholt]

@LukasHebing : I implemented your suggestions. It is ready for rereview ;)

[LukasHebing]

Great, good example :)