Retrieve secrets from AWS SSM

[Costi Muraru]

Similar to the Vault integration: https://github.com/adobe/ops-cli#secrets-management
Make it possible to define something like this in the cluster.yaml file:

db_password: "{{ '/my/ssm/path/' | read_ssm(aws_profile='myprofile') }}"

https://docs.aws.amazon.com/systems-manager/latest/userguide/what-is-systems-manager.html