Resolvable environment hints for tasks and workflow nodes

[tclose]

Would like a way to specify the type of environment at the workflow level and have it propagate the nodes within the workflow.

Was thinking that nodes (and task definitions too), could specify a series of "environment hints", which will typically be an address to a Docker image I imagine, but can be any arbitrary string. Environment classes can then use these however they wish to resolve to an actually Environment instance via a from_hints() classmethod