Allow to customize QueueBufferConfig instances

[flozano]

I would like to use a version of QueueBufferConfig that can be reconfigured. QueueBufferConfig is not final, so with just this small change I can hook what I need to allow things like maxBatchOpenMs to be dynamically redefined for existing/new buffers.

Description of changes:

Just allow to override QueueBufferConfig copy instantiation.

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