Removing max_size on queue and add concurrency limit to 2

This implementation brings about the removal of the queue limiter and competition for up to two generations at the same time (I believe the machine can handle it - NOT SURE OF THAT)

app.py

@@ -111,5 +111,5 @@ with gr.Blocks() as demo:
         cache_examples=true_for_shared_ui
     )
 
-demo.queue(max_size=15)
+demo.queue(max_size=None, concurrency_limit=2)
 demo.launch(share=True)