Add Terraform configuration for Orthanc

[rbreslow]

Right now, the Terraform configuration for Orthanc lives in a few places:

• https://github.com/d3b-center/d3b-orthanc
• https://github.com/d3b-center/aws-infra-d3b-accounts/tree/master/postgresql-instances/orthanc-d3b-internal-db/chopd3bPrdHippa/prd

Since this ETL is one of the primary consumers of the Orthanc server, I think we should consider moving its Terraform configuration into this repository. In addition, after identifying any bottlenecks in the Orthanc <---> RDS flow (#38), we should consider running Orthanc in ECS to take advantage of scaling/make it easier to swap out the underlying instance type.