Add Graph description messages to rosgraph_msgs

[emersonknapp]

Description

Fixes #182

Add new message definitions to rosgraph_msgs that can be used to describe a running or potential ROS Graph.

• Graph: a list of nodes
• Node : describe a single node's parameters and interface endpoints
• Topic: describe a single topic endpoint, either Publisher or Subscription
• Service: describe a single service endpoint, either Server or Client
• Action: describe a single action endpoint, either Server or Client
• QoSProfile: describe a QoS Profile, either offered or requested
• InterfaceType: identify a rosidl type
• TypeHash: identify a REP-2016 RIHS type hash (rosidl_runtime_c defined type)

This is intended to supplant the definitions in use at https://github.com/ros-tooling/graph-monitor/tree/main/rosgraph_monitor_msgs

Is this user-facing behavior change?

Yes

Did you use Generative AI?

No

Additional Information

Part of the NoDL and rosgraph_monitor work being done within the ROSGraph Working Group.

We would like to get these messages into the core for Lyrical, so that we can build tools around them for release into that LTS distro.

These messages act as a counterpart to the NoDL schema, being used to output either a desired or observed state of a ROS application as a message between nodes. The NoDL schema is not a strict duplicate of the information that these messages will contain, because:

1. NoDL will contain information relevant to code generation that is of more detail than can be observed by graph inspection
2. These messages contain fields about "instantiated values" that do not exist at specification time, such as actual parameter values.
3. The contents of these messages generally refer to resolved fully-qualified graph names after namespacing and remapping are applied, something that is not known or relevant at the node specification level.