add medclip example

examples/medical_image_classification_medclip.py

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+from PIL import Image 
+from pyhealth.models.medclip_zeroshot import * 
+
+# STEP 1: load data
+image = Image.open('/home/wuzijian1231/Datasets/MedCLIP/example_data/view1_frontal.jpg')
+processor = MedCLIPProcessor()
+inputs = processor(images=image, return_tensors="pt")
+
+# STEP 2: define model
+model = MedCLIPModel(vision_cls=MedCLIPVisionModelViT)
+model.from_pretrained()
+clf = PromptClassifier(model, ensemble=True)
+clf.cuda()
+
+# STEP 3: define prompts
+cls_prompts = process_class_prompts(generate_chexpert_class_prompts(n=10))
+inputs['prompt_inputs'] = cls_prompts
+
+# STEP 4: make classification
+output = clf(**inputs)
+print(output)