middleware util: use regex pattern

Author: alukach

src/stac_auth_proxy/utils/middleware.py

@@ -30,7 +30,9 @@ def should_transform_response(self, request: Request) -> bool:
         -------
             bool: True if the response should be transformed
         """
-        return request.headers.get("accept") == "application/json"
+        return bool(
+            re.match(self.json_content_type_expr, request.headers.get("accept", ""))
+        )
 
     @abstractmethod
     def transform_json(self, data: Any) -> Any: