Package and push to Test PyPI every commit

[karalekas]

Install twine in the CI and drop the creds into protected GitLab variables.

Do some version magic to append the short commit hash to the __version__ string.

Good way to de-risk people unknowingly breaking the setup.py.

Also aids in automated integration testing with QCS.

References:

• https://test.pypi.org/project/pyquil/
• https://medium.com/@pypripackages/using-gitlab-pipelines-to-deploy-python-packages-in-production-and-staging-environments-8ab7dc979274