Move to GitHub actions / reusable actions

[arokem]

Just discussed the possibility of moving to GHA with @skoudoro. He mentioned that one of the issues with this move is that for a particular workflow, if one of the sub-workflows in your matrix fails, there's no way to restart just that sub-workflow and you have to restart all of the sub-workflows in your matrix, which is a pain. Looking around a bit, we found this page: https://docs.github.com/en/actions/learn-github-actions/reusing-workflows, which suggests that there is a way to create a template for a workflow that can then be reused across multiple separate workflows, that each have their own trigger. So, that could be a way forward on that.