Need to publish `azure-cli-testsdk` to PyPI

[tjprescott]

This is needed to support running or writing tests for extensions without cloning the CLI repository.

[yugangw-msft]

@tjprescott, is this the azedv work?

[tjprescott]

Currently azdev clones and installs the testsdk from source. If we wanted to avoid that, we could publish the package, if not on pypi, at least in some storage location where we could simply install the WHL file. It's not an urgent issue. Once published, azdev would be changed to use the WHL file instead of cloning and installing from source.

[ctaggart]

It would really be helpful if we could download it from https://pypi.org/project/azure-cli-testsdk/ . Some examples for using it would also be very welcome.

[yonzhan]

add to S164.