Setup a github actions workflow

[kmadisa]

Adding a workflow file to set up github actions to run the automated unit tests. The workflow uses a different docker image (hosted on https://nexus.engageska-portugal.pt/) that has been created and maintained by the SKA System Team.

NB: Docker image artefact will move to https://artefact.skatelescope.org/ in future!!!

Some of the unit tests were reworked by mock patching the call to helper_module.get_database so that they wouldn't need a running instance of the tango-db server. With that in place, the Jenkinsfile was also update to use the camtango_nodb_bionic docker image.

Also added a workflow, publish_to_pypi.yaml, to automate the process of publishing the Python package to PyPI when a tag is created. For more information on the action used to upload to PyPI, see https://github.com/marketplace/actions/pypi-publish.

For more information on github actions, see link.

Screenshots or code snippets (if appropriate):

• N/A

Definition of Done Checklist

• [x] Code meets our python style guidelines?
• [x] Unit tested (coded, passed, included)?
• [x] Requested at least 2 reviewers?
• [x] Commented code, particularly in hard-to-understand areas?
• [x] Made corresponding changes to the documentation (e.g. Python documentation, System Engineering Documentation, version description updates, README file, etc)?

JIRA: N/A

[kmadisa]

• [x] Add a static analysis step/job to ensure consistency with the Jenkins pipeline.

[kmadisa]

The https://nexus.engageska-portugal.pt/ service is currently down due to some upgrades (might take days).

• [x] Re-run workflow.

[kmadisa]

See https://github.com/ska-sa/tango-simlib/runs/2771488752?check_suite_focus=true for linting failure dummy test.