✨(back) manage streaming with the ai service

We want to handle both streaming or not when interacting with the AI
backend service.

src/backend/core/api/viewsets.py

@@ -1857,8 +1857,20 @@ class DocumentViewSet(
         serializer = serializers.AIProxySerializer(data=request.data)
         serializer.is_valid(raise_exception=True)
 
-        response = AIService().proxy(request.data)
-        return drf.response.Response(response, status=drf.status.HTTP_200_OK)
+        ai_service = AIService()
+
+        if settings.AI_STREAM:
+            return StreamingHttpResponse(
+                ai_service.stream(request.data),
+                content_type="text/event-stream",
+                status=drf.status.HTTP_200_OK,
+            )
+
+        ai_response = ai_service.proxy(request.data)
+        return drf.response.Response(
+            ai_response.model_dump(),
+            status=drf.status.HTTP_200_OK,
+        )
 
     @drf.decorators.action(
         detail=True,
@@ -2557,6 +2569,7 @@ class ConfigView(drf.views.APIView):
         array_settings = [
             "AI_BOT",
             "AI_FEATURE_ENABLED",
+            "AI_STREAM",
             "API_USERS_SEARCH_QUERY_MIN_LENGTH",
             "COLLABORATION_WS_URL",
             "COLLABORATION_WS_NOT_CONNECTED_READY_ONLY",