Added support for images (#609)

app/MindWork AI Studio/Provider/OpenAI/SubContentImageUrlData.cs

@@ -0,0 +1,17 @@
+namespace AIStudio.Provider.OpenAI;
+
+/// <summary>
+/// Represents the inner object of a nested image URL sub-content.
+/// </summary>
+/// <remarks>
+/// This record is used when the provider expects the format:
+/// <code>
+/// { "type": "image_url", "image_url": { "url": "data:image/jpeg;base64,..." } }
+/// </code>
+/// This class represents the inner <c>{ "url": "..." }</c> part.
+/// </remarks>
+public record SubContentImageUrlData : ISubContentImageUrl
+{
+    /// <inheritdoc />
+    public string Url { get; init; } = string.Empty;
+}