Update terraform/test.secure_agent.tfvars, terraform/network.tf, terraform/autoscaling-group.tf, terraform/efs.tf

To limit the amount of changes of each deployment, and make sure the AMI used in the LC is appropriate for the given region, I added it to a variable.

* In order to increase disk space allocated for Docker container utilize Amazon Linux 2. By default Amazon Linux 2 uses `overlay2` storage driver, which gives the base storage size of the space left on the disk.
* Removed SSM agent as it's shipped with all Amazon Linux 2 AMIs.
* Utilized `SSM` param store for storing `IICS` user credentials.
* Increased `EBS` volume size to allocate more disk space.

* Adjusted the instance to be a `t2.xlarge` since we are going to have more load.
* Increased container memory to 15 GiB.
* Increased EC2 instance's EBS root volume to 40 GB.
* Re-named the profile to indicate the environment it's associated to.

* Added a configurable hostname for container.
* Now everything from agent's home is mounted into a EFS file system for persistence.
* Added documentation on how to use this Secure Agent infra.
* Extracted role and profile for prod environment

This volume will act as the persistence storage for Secure Agent's logs and configurations.