Use patched async-openai library to work around a few upstream issues

Related to:

- CreateImageEditRequest forces an application/octet-stream content type
  for images (https://github.com/64bit/async-openai/issues/364)

- CreateImageEditRequest only deals with a single image
  (https://github.com/64bit/async-openai/issues/363)

This is a continuation of 8f86289373
and fixes the Image Editing feature for OpenAI.

src/agent/provider/entity/image.rs

@@ -58,6 +58,7 @@ impl From<ImageSource> for async_openai::types::ImageInput {
         async_openai::types::ImageInput::from_vec_u8(
             value.filename,
             value.bytes,
+            value.mime_type.to_string(),
         )
     }
 }