Add github action workflow

[katilp]

@stwunsch Would you be able to add a GitHub action workflow (e.g. as in https://github.com/cms-opendata-analyses/HiggsTauTauNanoAODOutreachAnalysis/blob/master/.github/workflows/main.yml)?

As a first test (i.e. before moving the files) they can be read from the current area and we then change to point to the final location.

This can be run with a small subset of data (depends on the time it takes to run). If so, the resulting plots are obviously the final ones but that's fine for test.