Weathertop POC: Slack integration to notify failures

[ford-at-aws]

Create a Slack webhook to which an event in AWS publishes notifications about test-related events. Specifically, these events should represent per-language errors on a per-run basis (runs will be 1x/weekly on schedule). They should appear on a dedicated Slack channel with a summary of the run, including:

• total test cases successful
• total failed
• total skipped (if possible)
• a link to the test cases for this run, pre-filtered without additional authentication (e.g. on Wiki)
• an updated label on our repo for percentage of tests passing (bonus)

Research

• Meeting w/ Alejandro Mera: this is OK. Follow the process
• Based on Slack App guidelines above, we have lots of fun interactivity options
• We will need AppSec approval

Team feedback:

• Something like: "Weathertop report: All tests passing! :white_check_mark: detailed report"
• When the occasional test does fail, I would like to see it say instead something like: "Weathertop report: PHP test problems! Ruby test problems!
  :gr-redcard: click here to see the detailed report" I don't need/want another channel, nor do I want to see # of tests on every run. A simple pass/fail with the relevant users and languages listed. I suppose the @ tags could be optional for the devs, but I would personally want to be pinged if my tests were failing.
• could it tag the language owner, maybe?