MoveGroupInterface does not provide any way to query execution state.

[liarokapisv]

Is your feature request related to a problem? Please describe.

Before the ROS2 port, the MoveGroupInterface::getMoveGroupClient returned an actionlib::SimpleActionClient instance which provided state querying capabilities. After the port, it now returns an rclcpp_action::Client instance, which doesn't provide any way to query state. This means one can't properly use the asyncExecute method in practice. As an example, we had issues using the async version for BehaviorTree integration. Instead we had to wrap the blocking version with a thread and do our own state keeping, complicating the solution.

Describe the solution you'd like

Some locals are used in the execute method in order to track execution, perhaps those could turn into member variables and some simple minimal state querying memebr functions could be added. Another approach would be to create a wrapper over the rclcpp_action::Client in order to provide access to current state execution.

[liarokapisv]

Closing in favor of #3160