Modify service module to accept camelCase parameters

[lancehampton]

For initial testing we prefer to use the container-definition submodule separately to create and manage container definitions. This is because

1. We can more easily create an interface where the developer provides information for each of their container definitions and we then turn that into task and service definitions that comply with our platform spec.
2. It is easier to manage the configuration of each container definition outside of the service module block, e.g. as separate .tf files.

However, the service module that receives the container definitions accepts parameters in snake_case, while the container_definition output of each container definition is a JSON object where the parameters are camelCase (same as the ECS API).

Since we would prefer to use that JSON output from each container definition the service module needs to be modified to take camelCase.

[lancehampton]

Will not implement. Will utilize terraform-aws-modules/terraform-aws-ecs as-is and modify our deployment pattern to suit. Customer can supply container definitions(s) via tfvars or similar. The upstream modules are great and we don't yet need enough customizations to justify taking on our own fork.