experimental: add getStatusTopic method to retrieve action status

[ikwilnaarhuisman]

#1145 <- issue (which this PR fixes 50% of)

AFAIK the status of an action (aka the topic) is always defined in the same way: /{ACTION_NAME}/_action/status with message type action_msgs/msg/GoalStatusArray. So instead of having to create the topic yourself, you can just get it directly from the action.

This PR is experimental because I doubt that this is acceptable yet, but it works and gives a better idea than my vague description of the "missing functionality"

[ikwilnaarhuisman]

I want to achieve the same functionality for the feedback topic, but I'm not sure how considering the message type differs:

  getFeedbackTopic() {
    return new Topic<TFeedback>({
      ros: this.ros,
      name: `${this.name}/_action/feedback`,
      messageType: "", // <<<< unknown! doesn't even work.
    });
  }

// OR

  getFeedbackTopic(messageType: string) {
    return new Topic<TFeedback>({
      ros: this.ros,
      name: `${this.name}/_action/feedback`,
      messageType: messageType, // works, but feels dirty.
    });
  }

[ikwilnaarhuisman]

@EzraBrooks What's your opinion on this?