[Feature request]: Add support for image generation/editing models

[rensftw]

It would be really cool to support image generation and/or image editing models via this plugin.
For example: dall-e-2 and dall-e-3 reuse the same OpenAI API key as regular GPT models. (docs).

Currently, when I manually set the model setting to dall-e-3 I get this response:

But I am successfully generating an image if I manually query OpenAI via curl

Proposal:

• By default the plugin's response to a prompt is to print the revised_prompt and the newly saved image path + filename.
• By default the plugin saves all image responses to some location.
  • Default value for this download location is set via the config object.
  • Optionally this can be toggled off, and user will have to open URLs with gx to preview images.
• When using dall-e-2/dall-e-3 the plugin can accept a new setting for the filesystem path where artifacts can be saved.
  • This way, you can use separate directories for different "visions" or projects