fix: add error logging for container creation failures

[yxf0314]

Without outputting the specific error from the exception, users cannot determine the reason for workload creation failure through GPUStack's model logs.

[Copilot]

Pull Request Overview

Adds explicit error logging when Docker container creation fails so users can see the underlying exception in GPUStack model logs.

• Add logger.exception calls in three container-creation code paths.
• Keep existing OperationError wrapping unchanged for upstream handling.

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