github publish hawc client

[shapiromatron]

Automatically publish hawc-client to pypi when a branch is tagged with a hawc-client tag.

In addition to changes in this PR:

• Create a new github environment named publish, and restrict to the main branch
• Add a secret to the PUBLISH_PYPI environment variable

As an example, see this action which resulted in a complete push to test pypi; the final PR made some changes to limit when this can be executed, and only push from the main branch.

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Reference:

• https://blog.pypi.org/posts/2023-04-20-introducing-trusted-publishers/
• https://github.com/pypa/gh-action-pypi-publish
• https://docs.github.com/en/actions/managing-workflow-runs-and-deployments/managing-deployments/managing-environments-for-deployment

[rabstejnek]

Looks good!