Expose --params-file option to composable nodes

[dawonn-haval]

Bug report

Moving from ros2/launch_ros#156

Upgrading from Dashing to Foxy broke my parameter.yaml files that I was using in a composable node. After some debugging I found out that the composable node manager has it's own method for loading parameters from a yaml file that is different from rclcpp's parameter yaml file loader that was used in Dashing. The 'new' file format does not support defining parameters for multiple nodes so I would like to expose the --params-file flag in the component manager service so that the prior logic can be used.

Required Info:

• Operating System: Ubuntu 20.04
• Installation type: Source
• Version or commit hash: 2.0.2, foxy, dc528ad
• DDS implementation: Fast-RTPS
• Client library (if applicable): N/A

Steps to reproduce issue

See ros2/launch_ros#156

Expected behavior

I should be able to use the params file from dashing with multiple nodes in one file.

Actual behavior

the file format has changed and only a single node per file is possible with the new format.

Additional information

Pull request incoming shortly.

[ivanpauno]

Closing in favor of ros2/launch_ros#156.