Adds GitHub Action based Jekyll build & deploy

[lenucksi]

Given the breakage in #232 I added a version of GitHub action based site build based on https://github.com/helaili/jekyll-action and https://jekyllrb.com/docs/continuous-integration/github-actions/

This publishes to the gh-pages-ghactions branch to not overwrite the working Travis version. I'll PR this to the .net repo too and switch the site generation to the other branch there to see if it works.

The Jekyll action is pinned to a specific commit due to this: helaili/jekyll-action#60 (comment)

We could

• switch Ubuntu to latest
• should add this to pull requests.

Please take a look and see if this suffices to replace our Travis build and remove the Gemfile.lock and Ruby version issues we keep having. Also pinging @StingRayZA

[lenucksi]

Looks like this builds mostly clean as can be seen on https://github.com/InnerSourceCommons/innersourcecommons.net/tree/gh-pages-ghactions and https://innersourcecommons.net

[dicortazar]

@lenucksi , it seems there are some conflicts to resolve. Is this something you can help with?

[lenucksi]

@lenucksi , it seems there are some conflicts to resolve. Is this something you can help with?

Resolved the conflicts. Ready to merge. Needs adaptation of the served branch afterwards though.