[Java] Allow Ray actors to start in a different namespace than the driver in Java API

[shrekris-anyscale]

Description

The Java API should allow Ray actors to start in a different namespace than the driver.

In Python, this is allowed using the actor options. E.g.:

ray.init(namespace="driver-namespace")

@ray.remote(namespace="actor-namespace")
class ExampleActor:
    ...

# Starts ExampleActor in the
# "actor-namespace" namespace
ExampleActor.remote()

More context can be found here.

Use case

This provides finer-grained control over Ray actor behavior. Ray applications can make assumptions about their actors' namespaces regardless of the driver namespace.

[simon-mo]

@raulchen can this be part of Ray 2.0 (branch cut 06/22 for beta and 7/22 for final)? This doesn't necessarily block #22726 but would be necessary for Ray Serve Java API's public release. Thank you!

[raulchen]

@simon-mo This change should be simple. I'll ask @jovany-wang to work on this when he come back to work next week. Probably it will be done after 6/22, but definitely before 7/22.

[simon-mo]

Awesome thanks!

[jovany-wang]

Duplicate to #22563