Variable for ephemeral_storage in aws_ecs_task_definition

[jkuypers93]

Hello,

I would like to increase the ephemeral_storage of a Metaflow ECS task so that it can load larger Docker images (Pytorch GPU Docker images are 10Gb+ compressed). Currently, the instance runs out of disk space and shows the following error:

CannotPullContainerError: no space left on device

The ephemeral_storage is currently not defined in the metadata-service submodule so it is set to its default value of 21Gb - would it be possible to have a variable so that we can define this parameter?

I'd be happy to work on this and share a PR.

Many thanks!

[jkuypers93]

Opened PR #86