Description

In cases like this where users are trying to start a workflow that already exists, they should see a 400 error code to indicate that this is a "bad" request that they are trying to perform. A 500 response code is extreme here in the case that this is a client side error.

{"errorCode":"ERR_START_WORKFLOW","message":"error starting workflow 'SimpleWorkflow': unable to start workflow: failed to start orchestration: error from internal actor: an active workflow with ID 'SimpleWorkflow' already exists"}

where would be the best place to add tests for this change? @cicoyle @JoshVanL

Issue reference

Please reference the issue this PR will close: #[issue number]

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Unit tests passing
• End-to-end tests passing
• Extended the documentation / Created issue in the https://github.com/dapr/docs/ repo: dapr/docs#[issue number]
• Specification has been updated / Created issue in the https://github.com/dapr/docs/ repo: dapr/docs#[issue number]
• Provided sample for the feature / Created issue in the https://github.com/dapr/docs/ repo: dapr/docs#[issue number]