Add --lora_alpha and metadata handling to train_dreambooth_lora_sd3.py

[arnav-roy]

What does this PR do?

Fixes #11730

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[arnav-roy]

@linoytsaban Please review

[linoytsaban]

thanks @arnav-roy! I see lora_alpha is missing from the text_encoder config, other than that I think we're good :)

diffusers/examples/dreambooth/train_dreambooth_lora_sd3.py

Lines 1283 to 1289 in cf127dd

	if args.train_text_encoder:
	text_lora_config = LoraConfig(
	r=args.rank,
	lora_alpha=args.rank,
	lora_dropout=args.lora_dropout,
	init_lora_weights="gaussian",
	target_modules=["q_proj", "k_proj", "v_proj", "out_proj"],

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