Allow loading any document in some assistants (#508)

Co-authored-by: krut_ni <nils.kruthoff@dlr.de>
Co-authored-by: Thorsten Sommer <mail@tsommer.org>

app/MindWork AI Studio/Tools/ContentStreamPdfMetadata.cs

@@ -0,0 +1,11 @@
+using System.Text.Json.Serialization;
+
+namespace AIStudio.Tools;
+
+// ReSharper disable UnusedAutoPropertyAccessor.Global
+// ReSharper disable ClassNeverInstantiated.Global
+public sealed class ContentStreamPdfMetadata : ContentStreamSseMetadata
+{
+    [JsonPropertyName("Pdf")] 
+    public ContentStreamPdfDetails? Pdf { get; init; }
+}