Propose a new sample code for the ch09/peformance section that creates a HAR file using `mitmproxy`

[kazurayam]

I could make an alternative sample code that creates a HAR file using the mitmproxy

https://github.com/kazurayam/mitmproxy-lesson

So, let me add a new sample code for the book.

[kazurayam]

I added 4 class files of .ch09.performance.HarCreatorMitmTest

[kazurayam]

I would leave this branch unmerged into the develop branch.
I would wait if @bonigarcia expresses his thinking how would look at the problem of "HarCreator*Test" problem.