Proposal: Add ability to optionally localize input files for tasks

[vsmalladi]

Problem:
Cromwell's GCP backend supports optional localization of files, such as in this example:
https://github.com/broadinstitute/warp/blob/2b0493125cae26b71fb8eecf278d63104c573772/tasks/broad/ImputationTasks.wdl#L95

Add the ability to choose to localize or stream files for tasks.

Solution
Add in new localize variable to tesInputs

Linked to this issue: microsoft/CromwellOnAzure#419

[kellrott]

I believe this overlaps with issue #156 and PR #157

[vsmalladi]

@kellrott Yes it seems to. We might want to discuss what the best term to call this is and what the default behavior is between streaming and localizing.

Adding @MattMcL4475 to the discussion.

[vsmalladi]

closing issue will be covered by issue #156 and PR #157