feat(utils.py): support google kms for secret management

https://github.com/BerriAI/litellm/issues/1235

litellm/proxy/example_config_yaml/custom_auth.py

@@ -0,0 +1,16 @@
+from litellm.proxy._types import UserAPIKeyAuth
+from fastapi import Request
+from dotenv import load_dotenv
+import os
+
+load_dotenv()
+
+
+async def user_api_key_auth(request: Request, api_key: str) -> UserAPIKeyAuth:
+    try:
+        modified_master_key = f"{os.getenv('PROXY_MASTER_KEY')}-1234"
+        if api_key == modified_master_key:
+            return UserAPIKeyAuth(api_key=api_key)
+        raise Exception
+    except:
+        raise Exception