Add an option to not capture stdout and stderr

[Hugal31]

Description

When using ExecuteProcess and its childs, the current mechanism to capture the stdout and re-emit it with a prefix is fine. However, I would like an option to not capture those output.

Motivation

We are using systemd-journal to monitor our logs, and it comes with the added benefit kinda structured logs:
you can filter by executable, command line, stdout vs stderr, etc...

However, by stepping between the difference processes and journald, launch removes this kind of information and add the process name in the MESSAGE field of the journal entry instead of using another variable.

Design / Implementation Considerations

It would probably mean to update osrf_pycommon as well to be able to pass the correct stdout/stderr values to loop.subprocess_exec.

Additional Information

No response

[wjwwood]

Seems reasonable to have this option, but just note that launch events that operate on stdout/stderr will no longer work.

A more complete solution would be to have it not capture, but instead get the output via systemd-journal or whatever you're using to capture and organize the output, so that launch can also use it.

[ros-discourse]

This issue has been mentioned on Open Robotics Discourse. There might be relevant details there:

https://discourse.ros.org/t/ros-news-for-the-week-of-july-7th-2025/45175/1