Add CloudFormation Rollback Alarms/Triggers

[brettstack]

CloudFormation should automatically roll back when the 5xx alarms fire.

[brettstack]

Documentation here https://docs.aws.amazon.com/AWSCloudFormation/latest/APIReference/API_RollbackConfiguration.html

We'll need to add this as a top-level entry to serverless.yaml and add the correct Alarm resources

RollbackConfiguration:
  MonitoringTimeInMinutes: 30
  RollbackTriggers:
  - Arn: !GetAtt MyAlarm.Arn
    Type: AWS::CloudWatch::Alarm
  - Arn: !GetAtt MySecondAlarm.Arn
    Type: AWS::CloudWatch::Alarm

[brettstack]

We have some basic alarms defined using a Serverless Framework Plugin https://github.com/wizeline/serverless-fullstack/blob/master/serverless.yaml#L118. You'll need to look at the generated CloudFormation template to discover the correct names of the AWS::CloudWatch::Alarm Resources