Links deployment confidence dashboard on deploy creation msg (#28)

Links deployment confidence dashboard on deploy creation msg

While deploying it is important that we check the vitals on our services to ensure
nothing we've deployed is breaking.

This commit adds support for linking a deployment confidence dashboard to allow us to do just that.

Author: tiagonbotelho

action.yml

@@ -38,6 +38,9 @@ inputs:
   slack_channel:
     required: false
     description: name of channel to post deployment completion messages
+  deployment_confidence_url:
+    required: false
+    description: link for the deployment confidence dashboard
 runs:
   using: 'node12'
   main: 'dist/main/index.js'