Create GitHub Actions CI pipeline to update generated code via CIMgen

[stv0g]

It would be a neat addition to automatically trigger a workflow in the cimpy (and possibly also CIMpp) repos whenever a new CIMgen version has been released.

This workflow should then use the updated CIMgen version to regenerated the Python classes in the cimpy.cgmes_* packages.

This workflow could be triggered automatically from a corresponding release workflow in the CIMgen repo.

This workflow can commit and push the updated generated code to this repo and bump its version.