[RFC] Remind people about uncommented and unmerged PRs assigned to them

[orta]

Proposal:

Create a GitHub team in our org of people who are interested in getting notifications. Every hour, Peril loops through these people, sees if they have assigned open PRs which that they haven't interacted on.

Peril can then poke them on slack about the PR.

Reasoning

We used to have something like this, now we don't. Now it feels like my PRs get hung by others and I have to remind people that they exist. It was much easier before to send PRs to people who are not actively watching a particular project.

Exceptions:

If you're not in the group, you don't get the message. It'd be opt-in. We can migrate anyone who signed up to the old slackbot by default.

Additional Context:

• We can grab slack IDs for someone via team.artsy.net.