Set gpu per model

[eliteprox]

What does this pull request do? Explain your changes. (required)

Adds the ability to set preferred gpu by model in the aimodels config.

    {
        "pipeline": "text-to-image",
        "model_id": "SG161222/RealVisXL_V4.0_Lightning",
        "price_per_unit": 190000,
        "warm": false,
        "gpus": [0]
    },

Linked to changes in livepeer/ai-worker#111

Specific updates (required)

How did you test each of these updates (required)

Does this pull request close any open issues?

AI-134

Checklist:

• Read the contribution guide
• make runs successfully
• All tests in ./test.sh pass
• README and other documentation updated
• Pending changelog updated