Add github actions config yml

[nkrusch]

Extension CLI allows pulling config files into a project using xt-sync.

It currently allows pulling in CI configs for gitlab and travis. It should also have an option for github actions and (possibly?) circle-ci.

Side note: the command name should probably better describe this functionality, since what is does is "pull in latest config/config starter code", which is slightly different in semantics from the original use case. Maybe rename to xt-config? Besides CI configs, it also has option for eslint config and gitignore matching default project organization.

For added value could also add in user guide, how to configure the CI to upload to store(s) automatically.