In case of existing workflow both sync and async executions should have an option to error out or return an existing execution

In addition to WorkflowReusePolicy, GoSDK has a flag

https://github.com/temporalio/sdk-go/blob/57736850f55b2b3e17cffa0e3493c4e0d6de831f/internal/client.go#L529

// When WorkflowExecutionErrorWhenAlreadyStarted is true, Client.ExecuteWorkflow will return an error if the
// workflow id has already been used and WorkflowIDReusePolicy would disallow a re-run. If it is set to false,
// rather than erroring a WorkflowRun instance representing the current or last run will be returned.
//
// Optional: defaults to false
WorkflowExecutionErrorWhenAlreadyStarted bool

That enabled an explicit failing of the workflow start if WorkflowReusePolicy disallowed an execution instead of returning the old execution.

This has to be added to JavaSDK, otherwise, there is no way for users to get the fact that the start request was disallowed and the returned execution is an old execution.

One of the discussions on this topic:
C02E8TQA01G-1673406348.075879.txt

Compare the Go SDK flag in internal/client.go with the Java SDK's synchronous and asynchronous workflow-start entry points. Trace WorkflowReusePolicy handling and define completion as allowing both execution modes to either report a disallowed start as an error or return the existing execution, with corresponding behavior covered by the SDK's tests.