Add Github action

[fmauch]

This PR aims at adding a github action that could be included by other repos. At the time of creating this, there is a first working version that is probably not optimal (hence the draft), since I am rather new to the topic of writing custom actions.

You can see an example of this action being used here.

Obviously, the action could be moved to its own repository, as well, but I decided to include it here at least for a first, testable version.

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Edit: I've been thinking that from my point of view, this might actually a valid solution that could act as a first version. Whether or not we want to use a more versioned approach or move the action to its own repo is something to decide for the maintainers.

[ct2034]

Thank you for your contribution, @fmauch. To support this, I have fixed the versioning scheme for the package, which would then also be the version of the action that people could state when they use it, rather than the branch.
But I want to ask you to add a section and brief usage example to the README.md.

[fmauch]

I've added an action usage section to the main README. It uses the latest version currently being present on the main branch. @ct2034 Do you plan to add tags for each version?

Most actions that I know keep a major version tag running along the latest patch version. So in this case there would be a v1 tag pointing to the same commit as 1.1.5 at the time of writing. If you plan to also do this, we could reference @v1 inside the workflow definition. This is probably less brittle as you otherwise would have to bump the version in the workflow example in the README each time you do a patch release.

[ct2034]

Thanks again for the contribution. This looks awesome