WorkflowManager: extend workflow re-run condition check

[reisingerf]

When a workflow is retriggered via the API / UI the default behaviour should be to prevent reruns if the same request already exists, i.e. if the exact workflow inputs where already used in an earlier (on ongoing) workflow execution.

This is to prevent accidentally duplicated workflow run requests. Legitimate re-runs with the exact same input should still be possible, but should require additional actions or admin intervention.