Allow automation to communicate person responsible for it (CODEOWNERS)

[patcon]

In this evolving philosophy of community automation, I'm leaning toward:

4. Be clear about a point of contact for support. Don't assume people know to check Git commit history on code.

Right now, there's a convention of informally pointing out the code for the automation in each automated message in Slack. If someone is technically inclined, they can explore the code repo and see who wrote the code, but that's perhaps not obvious.

So the idea is to add parsing of the CODEOWNER file on GitHub, and use that (an email for starters) to resolve to a Slack username. Then, the templates and helpers for automated messages can make it simple to refer to the person responsible for the automation :)