The command only worked when running it inside the git repository.

Now, it works from everywhere, and the version is constructed using
the latest git tag and the SHA of the latest commit, which may help
with further debugging in future issues.

Renaming version_config to setuptools_git_versioning to be compliant with new plugin version.

Formatted the version when a git hash is present for a better readability.

The version is set in the setup.py file. This will be used for the tar.gz releases.
Snap version is also retrieved from setup.py too, so we avoid code repetition.