Currently Feathr only supports getting a single type of keys thru client.get_online_features or client.multi_get_online_features. Essentially they are just sending the HMGET commands to Redis, say for "product_id".

Per this discussion (https://feathrai.slack.com/archives/C036HEUQM08/p1658237223861509), it would be good to add a convenient API to get multiple type of keys, say get some "product_id" and get some "user_id" at once.