fix: improve feedback to user when submitting a workflow from the CLI w/o a serviceaccount specified

[bennycornelissen]

What was the issue?
When submitting a workflow using argo submit somefile.yaml, if the workflow does not explicitly specify a spec.serviceAccountName, the output of the command would look like this:

❯ argo submit workflow-artifact-repo-ref-test.yaml
Name:                artifactory-repository-ref-vp472
Namespace:           argo
ServiceAccount:      default
Status:              Pending
Created:             Thu Nov 18 15:24:57 +0100 (now)
Progress:

The important bit here is the ServiceAccount: default bit. In my case, I have configured a default ServiceAccount in the workflowDefaults section of the workflow-controller configmap. This means that my workflow will not run with ServiceAccount: default, but with the ServiceAccount I specified there. See the command below:

❯ argo get @latest
Name:                artifactory-repository-ref-vp472
Namespace:           argo
ServiceAccount:      argo-default-workflow
Status:              Succeeded
Conditions:
 PodRunning          False
 Completed           True

What did I change?
I changed the string that is returned as the value for serviceaccount when no serviceaccount is set. Instead of suggesting the workflow is using the default serviceaccount, it now specifies that no serviceaccount has been set, and we're using a default ServiceAccount instead.

Further context
This PR is the result of a Slack discussion between myself and @crenshaw-dev on this particular issue.

[crenshaw-dev]

I don't think I have any actual permissions in this org, but approved, lgtm. 😄

[terrytangyuan]

LGTM. Thanks for tracking it down! I'll wait for others to see if there's any concern about the change.