Add reusable workflow for building and publishing python packages with poetry

[raminqaf]

fixes #5

[yannick-roeder]

I think we should separate reusable workflows from composite actions inside the repository. We could use a directory structure like this for example:

actions
  bump-version
  helm-lint
  helm-release
workflows
 python-release-poetry

I would also rename release-python-poetry to python-release-poetry so that future python workflows will be alphabetically sorted together with this one

Additionally we should think about splitting the workflow up into smaller actions, so that individual parts of it can be reused as well

[raminqaf]

@yannick-roeder & @disrupted I applied the changes that we discussed yesterday. The PR is so far ready to review. Before you start the review some notes on the changes:

• I changed the structure of the repository a bit. The reusable workflows files need to be under this address: .github/workflows/<reusable-workflow-name>.yaml. In other words, the structure looks like this:

  actions
    bump-version
    helm-lint
    helm-release
    ...
  
  .github  
    workflows
     python-release-poetry.yaml
  

• Besides if we add more reusable workflows in the workflows folder the README.md file is going to get really messy. Any suggestions on how we can organize the workflows in better order?
• We should also consider creating a tag in the near future (e.g., v1). With this, we can version the composite actions in a proper way.
• Every composite action or workflow related to Python is starting with the prefix python-. I would like to keep that for the rest of the actions/workflows
• I also called the workflow from github-playground repo and it seems that everything is working properly. 🎊

[disrupted]

This looks really great! I just commented some minor nitpicks.

[disrupted]

I noticed that the changelog creation is not part of the workflow. Did you leave it out intentionally? Of course this could also be added in a followup, I think that this could be really useful to other projects too.

[yannick-roeder]

Yes, changelog generation would be nice for other projects as well. I think we can resolve that in a separate issue

[raminqaf]

@disrupted Yeah, I didn't add it here yet since it is complicated action and needs some configuration. I would also instead do it in a separate PR.

[disrupted]

LGTM

The changes and reviews are already commited