A timer that can be triggered a finite number of times.

Feature request

Feature description

There can be situations in which you would like to call a function a finite number of times within the (same period of time) and not to be called endlessly. For those kind of situations the proposal is to give the timers the option to select the number of times that the timer is triggered. An example of use can be a "One Shot Timer" (which was implemented in ROS 1).

Implementation considerations

Given that use case stated above, it is possible to add the feature by keeping track of the number of times the timer is being triggered and canceling it after the number of callbacks is completed. An example of this implementation can be found on the following fork:

• https://github.com/Voldivh/rclcpp/tree/voldivh/callback_counter

Start by comparing the current rclcpp timer API with the proposed implementation in the linked Voldivh/rclcpp fork. Determine how a finite callback count or one-shot timer should be exposed and cancelled, then add coverage showing that the timer stops after the requested number of triggers.