Add --lora_alpha and metadata handling for train_dreambooth_lora_hidream

[ParagEkbote]

What does this PR do?

Refs #11730

As described in the issue, I've updated the test and training scripts to making LoRA alpha also configurable and include the metadata handling as well. Could you please review the changes?

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@linoytsaban

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[linoytsaban]

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[ParagEkbote]

@linoytsaban I have added the missing params to fix the single failing test.

Could you please review?