argo-workflows create --only-json doesn't export sensor configuration

[kmrnag]

The code only exports the workflow template and does not export sensor configuration. There is a clear TODO for this

if only_json: obj.echo_always(str(flow), err=False, no_bold=True) # TODO: Support echo-ing Argo Events Sensor template

in the argo_workflows_cli

It is not hard to also call str on flow._sensor that has the compiled sensor, but outputting two json objects (one for flow and another for sensor) together as a valid json seems to be more problematic, without breaking the interface. Perhaps we can add a new option to only export json for the sensor "--only-sensor-json"?

There is a related open issue about only-json not exporting cron workflow. Introducing two new parameters "--only-cron-schedule-json" and "--only-sensor-json" (only one of these options can be true at a time) can help address these issues.

Will be happy to submit a PR as the fix will be relatively small.