workflowStopped event enhancement

Both successful workflows and stopped workflows are generating similar kind of events with 'reason' as 'WorkflowSucceeded'. There is no way to differentiate successful vs stopped events to trigger different down streams based on the status.

What change needs making?
Would like to see reason as 'workflowStopped' for stopped workflows.

# Use Cases
We are using [Argo events](https://argoproj.github.io/argo-events/concepts/architecture/) architecture. We are using K8s Resource eventsource, relying on these k8 events to trigger downstreams. Since we are relying on 'WorkflowSucceeded' , it is matching events for both successful and stopped workflows.

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**Message from the maintainers**:

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The issue names no files or tests; begin by tracing Kubernetes Resource events for successful and stopped workflows and their current reason values. Done means downstream consumers can distinguish the statuses, with stopped events using 'workflowStopped' and successful events retaining 'WorkflowSucceeded'.

Written by the indexing model from the issue text.