print the version and exit if env var ACTION has value VERSION

[tpokorra]

fixes #123

[CLAassistant]

All committers have signed the CLA.

[fkwp]

Hello @tpokorra and thx for your contribution.

Given that the service is currently controlled via env variables I am wondering if adding a cli lib only for the sake of a version feature is worth it. Also ideally we would infer the version string not manually maintained in an extra file but from git.

[tpokorra]

Given that the service is currently controlled via env variables I am wondering if adding a cli lib only for the sake of a version feature is worth it. Also ideally we would infer the version string not manually maintained in an extra file but from git.

Thank you for the suggestions.
I have now improved the pull request.