Alex MacLean

Add documentation for log format placeholders.

1

## Description This pull request adds documentation for the log format tokens (`{severity}`, `{function_name}`, etc.). It includes `{severity_with_color}`, a new token introduced in a [separate pull request](https://github.com/ros2/rcutils/pull/526). ### Did you...

Adds {severity_with_color} as a log format option.

12

## Description This change adds a new log formatting token option: `{severity_with_color}`. When used in the log format string, the severity level will be colorized in the log output, but...