Add support for dynamic, model-specific settings

[dsebastien]

When an image generation model is chosen, it should be possible to download the metadata of that model to discover how it can be configured: https://replicate.com/docs/reference/http#get-a-model-version

If we do that, then we could automatically generate the settings UI that matches the model in question. This would provide a better UX for configuring the plugin

Cfr #1

[dsebastien]

In addition, the settings should be stored under the key of the model name, enabling to keep the previous settings for a model when switching to another.

When a new model is chosen, the settings UI would change and would use the default values of the new model, or the previously saved ones for that model (if present).

Configuration wise, it could look like this:

imageGenerationConfiguration: {
  "black-forest-labs/flux-dev": {
     ...
  },
  "black-forest-labs/flux-pro": {
    ...
  },
  "stability-ai/sdxl": {
    ...
  }
}