Add controlled version of hist alpha set

[matthewfeickert]

Following PR #13, add example of a controlled hist alpha set

[matthewfeickert]

@coolalexzb Probably also worth looking through the pyhf source to see how this is done. https://github.com/scikit-hep/pyhf

[coolalexzb]

@matthewfeickert I think I am still unclear about which part of pyhf code might be useful except the random_histosets_alphasets_pair function I used before. I think what I need is only the structure of hist and alpha that users might use when they test interpolation function. One approach I come out with is that I can write the result of random_histosets_alphasets_pair function back to file and analyze the structure of input data and modify the logics of run.py script.