feat(proxy_cli.py): support json logs on proxy

allow user to enable 'json logs' for proxy server

litellm/proxy/_logging.py

@@ -0,0 +1,20 @@
+import json
+import logging
+from logging import Formatter
+
+
+class JsonFormatter(Formatter):
+    def __init__(self):
+        super(JsonFormatter, self).__init__()
+
+    def format(self, record):
+        json_record = {}
+        json_record["message"] = record.getMessage()
+        return json.dumps(json_record)
+
+
+logger = logging.root
+handler = logging.StreamHandler()
+handler.setFormatter(JsonFormatter())
+logger.handlers = [handler]
+logger.setLevel(logging.DEBUG)