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/ContentStreamSseEvent.cs

@@ -0,0 +1,15 @@
+using System.Text.Json.Serialization;
+
+namespace AIStudio.Tools;
+
+public sealed class ContentStreamSseEvent
+{
+    [JsonPropertyName("content")] 
+    public string? Content { get; init; }
+    
+    [JsonPropertyName("stream_id")] 
+    public string? StreamId { get; init; }
+
+    [JsonPropertyName("metadata")] 
+    public ContentStreamSseMetadata? Metadata { get; init; }
+}