Update handler.py

the following input is send to the endpoint with a post request.
```
{'json': {'inputs': 'a dog waiting for its companion to come.', 'parameters': {'negative_prompt': 'no dog', 'height': 512, 'width': 512, 'num_inference_steps': 25, 'guidance_scale': 7.5}}}
```

handler.py

@@ -9,15 +9,21 @@ class EndpointHandler:
         ).to("cuda")
 
     def __call__(self, data: Dict[str, Any]) -> List[Dict[str, Any]]:
-        inputs = data.pop("inputs")
-        prompt = inputs.pop("prompt", "dog")
-        guidance_scale = inputs.pop("guidance_scale", 4.5)
-        num_inference_steps = inputs.pop("num_inference_steps", 28)
-        seed = inputs.pop("seed", 0)
+        data = data.pop("json")
+        prompt = data.pop("inputs", None)
+        parameters = data.pop("parameters", {})
+        negative_prompt = parameters.pop("negative_prompt", "bad quality, worse quality, deformed")
+        height = parameters.pop("height", 512)
+        width = parameters.pop("width", 512)
+        guidance_scale = parameters.pop("guidance_scale", 4.5)
+        num_inference_steps = parameters.pop("num_inference_steps", 28)
+        seed = parameters.pop("seed", 0)
         
         prediction = self.pipeline(
             prompt, 
-            negative_prompt="bad quality, worse quality, deformed",
+            negative_prompt=negative_prompt,
+            height=height,
+            width=width,
             guidance_scale=guidance_scale, 
             num_inference_steps=num_inference_steps, 
             generator=torch.manual_seed(seed)