cpuPlatform default runtime attribute not configurable from Cromwell configuration

[hkeward]

It seems like the only default runtime attributes that Cromwell will pass through to tasks from its config are bootDiskSizeGb, noAddress, preemptible, and zones. We've tried setting a default in the Cromwell configuration for cpuPlatform but it does not appear to be applied to tasks. Setting this attribute on the runtime block of tasks directly works as expected.

Some regions don't have n1 machines, meaning we need to pass cpuPlatform for every task (or they will fail to start up).

Ideally we could set cpuPlatform in the default runtime attributes block in the Cromwell configuration file and have it pass through in the same way that the other GCP-specific attributes are.