Allow sharing of runconfigs

[dmjb]

Right now, we accept a variety of config options over the CLI or API and create a runconfig file specify all the options. In order to share configurations between developers, it would be useful to export and import runconfigs.

Proposed commands:

thv export <workload name> <path>
thv run --from-config <path>

Will export and import respectively. We need endpoints for the API which implements similar functionality.