Value of `x-ms-approximate-messages-count` header not returned in `queue.get_metadata()` result

[wilsonzlin]

It looks like QueueClient::get_metadata returns parsed headers in common_storage_response_headers which doesn't parse the value of x-ms-approximate-messages-count. We currently need access to this property for crucial infra monitoring and scaling purposes. Is there a way to access this value or the raw headers directly?