add workflow

[HeikoGr]

This is only an idea. Maybe a bad one...

this patch collects the json data from ENTSOG and GIE and process the junyper notebook as an github action. attention: the data is only stored temporary during the CI process and is transferred for publishing on github pages under the branch 'gh-pages'.

to use github pages you must enable them first: https://github.com/berthubert/gazproject/settings/pages

the workflow then deploys to: https://berthubert.github.io/gazproject/