Add Scheduled Tasks functionality for EC2 deployments.

[timbaileyjones]

Starting with v1.1.1 of mu, Scheduled Tasks can be configured via mu.yml file. However, the scope of #158 was to route CloudWatch events to ECS tasks, not EC2 instances.

As a result, users wanting Scheduled Tasks functionality must add provider: ecs to their mu file. This issue is a placeholder so we can plan this feature for EC2 also.