Automatically install the Kybra dfx extension

[lastmjs]

For simplicity and to get a release out quickly without spending too much time on it, we're not automatically installing the kybra extension for the developer. They will have to manually run python -m kybra install-dfx-extension. We should do this in some kind of pip install hook, I believe in setup.py, similar to how you use npm scripts in Azle to automatically install the extension.