cd: publish releases to PyPI with GA

[juarezr]

This PR has the objective of fixing the release to PyPI

Changes

1. Added new workflow using Github Actions
2. The workflow will be triggered when publishing a new release on Github
3. This assumes that:
   1. The master branch has no issues and builds with no error
   2. Testing and review of changes already happened using pull requests
   3. Changes are documented in docs/changes.rst
   4. There is a summary of the changes in the release description
4. Only release to PyPI is tackled in this PR
5. Conda-Forge and readthedocs.org will be fixed further
6. Testing on PR does not apply. This workflow will be tested with the release v1.7.6

Checklist

Checklist for pull requests including new code and/or changes to existing code...

• [ ] Code
  • [ ] Includes unit tests
  • [ ] New functions have docstrings with examples that can be run with doctest
  • [ ] New functions are included in API docs
  • [ ] Docstrings include notes for any changes to API or behaviour
  • [ ] All changes documented in docs/changes.rst
• [ ] Testing
  • [ ] Tested local against remote servers
  • [ ] Github Actions CI passes (unit tests run under Linux)
  • [ ] AppVeyor CI passes (unit tests run under Windows)
  • [ ] Unit test coverage has not decreased (see Coveralls)
• [ ] Changes
  • [ ] (Optional) Just a proof of concept
  • [X] (Optional) Work in progress
  • [X] Ready to review
  • [ ] Ready to merge

[coveralls]

Coverage remained the same at 91.759% when pulling a014a8a5c719fc82e91c938ba5794feeb2bbbf9b on juarezr:pypi-release-action into 46316476425318dcbad83d73730db4e4bdaaa160 on petl-developers:master.