create new package nav2_composition

[gezp]

Signed-off-by: zhenpeng ge zhenpeng.ge@qq.com

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Basic Info

Info	Please fill out this column
Ticket(s) this addresses	(tickets: #2147)
Primary OS tested on	(Ubuntu20.04, ROS 2 Galactic from binaries)
Robotic platform tested on	(gazebo simulation of turtlebot3)

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Description of contribution in a few bullet points

create a composition-based bringup package for Nav2, in other word, compose all Nav2 nodes in a single process instead of launching these nodes separately, which is useful for embedded systems users that need to make optimizations due to harsh resource constraints.

• create multiple nodes in a single main() (manual composition).
• create a bunch of single threaded executors to spin these nodes.

you can find some details about performance test(cpu and memory usage) here

• https://discourse.ros.org/t/nav2-composition/22175

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Future work that may be required in bullet points

try to enable intra-process comms until it's stable in ROS2, which are still kind of under development currently, you can find more detials:

• Allow intra-process communication to leverage full suite of QoS settings ros2/rclcpp#1753
• Status of today's ROS 2 message delivery mechanisms ros2/rclcpp#1750

For Maintainers:

• Check that any new parameters added are updated in navigation.ros.org
• Check that any significant change is added to the migration guide
• Check that any new functions have Doxygen added
• Check that any new features have test coverage
• Check that any new plugins is added to the plugins page
• If BT Node, Additionally: add to BT's XML index of nodes for groot, BT package's readme table, and BT library lists

[gezp]

It provides a composition-based bringup method, which could replace launching Nav2 nodes separately in package nav2_bringup, so it's not necessary to create a new package nav2_composition , just put it in package nav2_bringup.

The PR should be closed and new PR #2555 is created.