[postgres] Cannot reenter SubOrchestrator when it fails

[youngbupark]

CallSubOrchestrator doesn't work when it reenters after suborchestrator is failed with the following error.

orchestration-processor: failed to complete work item: orchestration instance already exists
github.com/microsoft/durabletask-go/backend.(*worker).processWorkItem
        /Users/youngbu.park/go/pkg/mod/github.com/microsoft/durabletask-go@v0.6.1-0.20250524005013-f1543590a4fb/backend/worker.go:244

postgres implementation doesn't have WithOrchestrationIdReusePolicy option while sqlite backend has this id reuse policy. After adding this, SubOrchestrator works as expected.

[youngbupark]

@cgillum Please review this issue and fix #104