[ros2action] Display info about action goals on an action server

Feature request

Feature description

Proposed originally in https://github.com/ros2/ros2cli/issues/202.

Add a goal verb for getting info about active or terminated goals for a given action server.

Proposed usage:

• List goals for a given action name. Output node names with action servers and goal IDs.

ros2 action goal list [--count] ACTION_NAME

E.g.

$ ros2 action goal list /fibonacci
/node/foo: 2
    152790028afb49a3b3c61383e6b97320
    8c3449e71c9941ed8ad3d68fdd7f553c
/another/node/bar: 1
    b07cb18ca2dc4cca95acfc131fc49223

$ ros2 action goal list --count /fibonacci
/node/foo: 2
/another/node/bar: 1

• Get details for a specific goal (request, result, status).

ros2 action goal info [--goal-only] [--status-only] [--result-only] ACTION_NAME GOAL_UUID

$ ros2 action goal info /fibonacci 152790028afb49a3b3c61383e6b97320
Goal:
  order: 5

Status: EXECUTING

$ ros2 action goal info /fibonacci 8c3449e71c9941ed8ad3d68fdd7f553c
Goal:
  order: 5

Status: SUCCEEDED

Result:
  sequence: [0, 1, 1, 2, 3]

Implementation considerations

I believe most of the proposed API should be feasible, except for accessing the goal request arguments, which requires adding some new API for getting this information to the rcl level.

Start with the proposed ros2 action goal list and ros2 action goal info entry points, then review the stated need for new rcl-level access to goal request arguments. Done means active and terminated goals can be listed and queried for their request, status, and result as described.