Support inputs/outputs in tasks

[xyhuang]

We want to support inputs/outputs in the tasks so that data can be transposed from/to external data sources (e.g. object storage). The inputs/outputs fields should be added under the task object, it should directly map to the inputs/outputs fields in the Argo CRD for "container" typed tasks, and if container is not specified it should default to use a "noop" container which allows user to perform only inputs/outputs.
One use case can be that user can use the "inputs" to pull configuration from remote object storage to managed experiment-volume, so that the workflow can pick it up to run the experiments. Then after experiment finishes user can use the "outputs" to push experiment results from the experiment-volume to the remote object storage so that it can be persisted in the cloud.

[xyhuang]

/assign