Transfer - Graceful stop does not stop immediately

[yahavi]

• All tests passed. If this feature is not already covered by the tests, I added new tests.
• All static analysis checks passed.
• This pull request is on the dev branch.
• I used gofmt for formatting the code before submitting the pull request.

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Fix 2 issues in the Graceful Stop mechanism of jf rt transfer-files command:

1. Create producerConsumerWrapper pointer in createTransferPhase to allow access it in StopGracefully:

func (pb *phaseBase) StopGracefully() {
	if pb.progressBar != nil {
		pb.progressBar.StopGracefully()
	}
	if pb.pcDetails != nil { // <- Was always nil
		pb.pcDetails.chunkBuilderProducerConsumer.Cancel(true)
		pb.pcDetails.chunkUploaderProducerConsumer.Cancel(true)
	}
}

2. Since the Graceful stop mechanism is async and we poll interruptIfRequested every 20 seconds, there is a chance that more than 1 interruption signal will be sent to the "stopSignal" channel. This will cause the code to freeze.

[github-actions]

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