Add a way to pass extra parameters to ros_gz_bridge (backport #628)

[mergify]

🎉 New feature

Closes #624

Summary

Added a new argument bridge_params to allow users to pass extra parameters to ros_gz_bridge when using the launch file. An example of these parameters would be qos_overrides
I have changed the node declarations to an opaque function so that I can get the value of bridge_params.
bridge_params is converted from string to dictionary and then passed to the parameters of the ros_gz_bridge node.
The way I have done all of this is complicated and so please do tell me if there is an easier way to do this.

Test it

To test this something like the following command can be used:
ros2 launch ros_gz_bridge ros_gz_bridge.launch.py bridge_name:=ros_gz_bridge config_file:=<path_to_your_YAML_file> bridge_params:="'qos_overrides./topic_name.publisher.durability': 'transient_local', 'qos_overrides./another_topic_name.publisher.durability': 'transient_local'"

Then to check if the qos overrides have applied:
ros2 topic info /topic_name --verbose
ros2 topic info /another_topic_name --verbose

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

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This is an automatic backport of pull request #628 done by Mergify.