Describe your feature request

It is already possible to give actors a name: https://docs.ray.io/en/master/actors.html#named-actors and to retrieve the actor handle via ray.get_actor("some_name").
It would however be very handy to have some kind of ray.list_named_actors() API method to get a list/dict of all currently available named actors.
It can be useful for:

• Better debugging

PrestoDB https://prestodb.io .. is widely used as SQL frontend for many different data-sources, including ElasticSearch, and even files in S3 .. would be very nice if there would be a Connector available for Vespa.

Currently the way that the predict function converts the incoming data and more importantly the return statement is quite obscure, and the community tends to just look at the util.py functions, however they shouldn't have the need to read the source to know what rules apply. For this it would be useful to ahve a table or a high level overview of the rules that apply in regards to what data types g