Add FLUX Control LoRA weight param

[RyanJDick]

Summary

Add the ability to control the weight of a FLUX Control LoRA.

Example

Original image:

Prompt: a scarecrow playing tennis
Weights: 0.4, 0.6, 0.8, 1.0

QA Instructions

• weight control changes strength of control image
• Test that results match across both quantized and non-quantized.

Merge Plan

Do not merge this PR yet.

1. Merge Support FLUX structural control LoRA models #7450
2. Merge LoRA refactor to enable FLUX control LoRAs w/ quantized tranformers #7446
3. Change target branch to main
4. Merge this branch.

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• Documentation added / updated (if applicable)
• Updated What's New copy (if doing a release after this PR)

[RyanJDick]

I think there is some additional metadata handling needed for the weight param, which I have neglected. @maryhipp or @psychedelicious can you help with that (and any other frontend stuff I may have missed).

[psychedelicious]

Because the weight setting is part of an individual canvas layer's state, it gets recalled along with the layer. No other changes required for that to work thankfully.