Backward Compatibility with ROS 2 Humble

[YuanYuYuan]

Description

This is a draft that backward supports Humble #303. It's currently based on #333.

Status

• Basic pub/sub works.
• The workflow should be changed to Humble.
• rclcpp test failures

30 - test_intra_process_manager (Failed)
53 - test_parameter (Failed)
56 - test_publisher (Failed)
61 - test_qos (Failed)
64 - test_qos_event (Failed)
91 - test_guard_condition (Failed)
92 - test_wait_set (Failed)

[clalancette]

So the way that we usually do this is to create a branch for each of the distributions. In this case, what we'll want to do is to create a humble branch, and then retarget this at that branch. However, I want to get some more of the major work landed on rolling before we make that branch. So I think this is appropriate as a draft for now.