Notify ourselves when build actions fail

[cnunciato]

We've had a couple of instances lately of failed docs builds that weren't known about until days later. We should probably add some messaging to notify ourselves (e.g., in the #builds channel) when a site build fails so we aren't relying on a human to notice something's gone wrong.

[susanev]

🙏 id prefer this get sent to #docs instead of #builds, or to have a specific channel made for this if possible

[cnunciato]

Quick note that we now have #website-notifications for these kinds of alerts.

[susanev]

@sean1588 has fixed this, yay!