Naive ros2 pub/sub should have test

[griswaldbrooks]

Need

In order to contrast writing a DI/naive ros2 test for pub/sub
As a developer
I want to see an naive test example that will correspond to a later DI version.

Acceptance Criteria

Scenario: ros2 naive pub/sub should have test
GIVEN we want to write a ros2 pub/sub test
WHEN looking for example
THEN one will exist in the naive/test directory

Tasks

• Port ros1/naive/test/incrementer_test.cpp to ros2
• Update readme to show cli commands for testing and expected result

Notes

Not sure if the canonical way currently has some form of launch file, or requires a Spinner object.
I get the impression they don't but I can't confirm that.
The ros2 action test doesn't seem to need it.

References:
https://github.com/PickNikRobotics/ros_testing_templates/blob/main/ros1/naive/test/incrementer_test.cpp