New module: publish to GitHub pages

[JohannesRudolph]

A new foundation level module could help us include a publishing workflow for "collie foundation docs" to deploy the generated vuepress page on GitHub pages.

This makes a lot of sense after
#109

At meshcloud we are already using this internally to publish documentation for our collie managed landing zones

[florianow]

#139 tested and included it as an option of the bootstrap. I removed the deploy spn.