Webhook receiver

In January GitHub deprecated “integrations”, which would send emails and IRC message whenever we had GitHub activity. We were told that GitHub Actions would be able to replace this functionality, though so far it’s not ready for us. They also let us keep email functionality on two repos, though this is only a temporary solution.

Instead of waiting for GitHub actions, we should build our own webhook receiver to receive these events and send emails/IRC messages for them. Such a system would also be useful for other services, like Prometheus and Kanboard, which also support webhooks.

This receiver would be a Python daemon running in Kubernetes. We’d configure it to send events to mailing lists, IRC, and possibly others.

A correction-- GitHub actually does send email notifications on all repos, but we still want this for IRC notifications in #rebuild-spam, and other services like Prometheus and Kanboard.