Better alerting

[yerdua]

Expected Behavior

• Add a new label to errors indicating if an error is serious or not (some ideas: severity with values critical, high, low or maybe severe with values true, false)
• Add a notification channel to Stackdriver for low severity errors. This should only post on Slack and does not notify on call people

Current Behavior

All errors have the same severity and it's hard to tell which errors are severe and which aren't