Lifecycle Publishers and Subscriptions should not be Discovered by the ROS 2 Network until Configured

[Amronos]

Description

Lifecycle Publishers and Subscriptions (being implemented with #2715) should not be discovered by the ROS 2 network until the Lifecycle Node has entered the inactive state (meaning it is configured)

This was originally brought up by @fujitatomoya in #2715 (comment).

Motivation

This will allow one to determine whether a node is actually publishing/subscribing to a particular topic. It doesn't make sense to list lifecycle nodes as publishing/subscribing to a specific topic when they haven't even been configured.

Design / Implementation Considerations

The following way to implement this has been suggested by @fujitatomoya in #2715 (comment):

for doing that, probably we need to have state control (configured, inactive) in SubscriberBase class and underlying implementations, and then on_configure callback, we can configure the subscription to be discovered.

Additional Information

No response

[MichaelOrlov]

To be discussed at the client WG meeting.
cc: @mjcarroll