Add pypi release github action

[nolanbconaway]

Closes #604

This action will run whenever a new release is published on github, and will publish the version to pypi. I tested locally by running all the command in my venv, but this action also works well for some of my other projects.

The last remaining item is that @alanmcruickshank needs to set up __token__ based authentication to PyPI and store the token password as a github secret called PYPI_TOKEN.

[dmateusp]

Would you mind adding documentation for the release process (letting future maintainers know that there is a workflow that runs on git tagging and the steps to tag and push a tag)

We should also note that the https://github.com/sqlfluff/sqlfluff/blob/master/src/sqlfluff/config.ini file needs to be kept up to date

[dmateusp]

Once there is documentation and the token, @nolanbconaway do you want to test it by releasing 0.4.0a2 ?

[nolanbconaway]

That sounds good! I noticed that we hadn't been releasing alpha versions to pypi though-- is that something we'll do going forward?

[NiallRees]

That sounds good! I noticed that we hadn't been releasing alpha versions to pypi though-- is that something we'll do going forward?

We did starting with 0.4.0a1 https://pypi.org/project/sqlfluff/0.4.0a1/

[nolanbconaway]

Docs added!

[alanmcruickshank]

This looks great. I've added the PyPi token, and I've also sent @nolanbconaway an invite on pypi to be one of the maintainers.

@nolanbconaway - how do you feel about merging this PR this weekend and then doing another dry run by releasing 0.4.0a2 as per @dmateusp comment?

[nolanbconaway]

This looks great. I've added the PyPi token, and I've also sent @nolanbconaway an invite on pypi to be one of the maintainers.

@nolanbconaway - how do you feel about merging this PR this weekend and then doing another dry run by releasing 0.4.0a2 as per @dmateusp comment?

You betcha!

[nolanbconaway]

@sqlfluff/sqlfluff-maintainers LMK when 0.4.0a2 is 🎉 ready and i'll give the automated release a shot