Github integration

[andrea-dintino]

We need this to integrate with our (and most people) existing workflow, that is:

• Subscribe to a repo
• Read issues
• Upon reading issue, create a workplan (L1 + L2)
• Request a human review on workplan (directly on Github or via e.g. Mattermost plugin)
• After the review, implement the workplan
• Submit a pull request with the implementation with a commit for each point of the workplan (L2)