Ability to pass artifacts from CLI

[jessesuen]

In the same manner which we can pass parameters to workflows, users should also be able to pass the location of an artifact as an argument. One use case is for submitting workflows using artifacts from a previous run (e.g. resubmit).

Artifact locations are structured data, so it is not as straightforward as key=value like it is with parameters. But we may be able to handle artifacts which have shorthand URLS and infer the datastructure from the URL. For example:

$ argo submit workflow.yaml -a myart=s3://mybucket.endpoint.com/path/to/art.tgz

$ argo submit workflow.yaml -a myart=https://storage.googleapis.com/kubernetes-release/release/v1.8.0/bin/linux/amd64/kubectl

In the S3 case, the URL does not incorporate credentials, so we may need to have to have special logic to somehow fill in the s3 credentials, possibly from the controller configmap.

Alternatively the entire artifact datstructure itself could be specified as json:

$ argo submit workflow.yaml -a myart=json='{"s3":{"bucket":"mybucket","endpoint":"endpoint.com","key":"path/to/art.tgz"}'