Workflow bot for optional PR workflows

[christophfroehlich]

That sounds nice. One possibility might be https://github.com/GregaVrbancic/gh-workflow-bot but that looks rather unmaintained. I think in the scope of this PR that might be over the top, we could keep that in mind for later, would you agree?

Originally posted by @fmauch in #21 (comment)

[christophfroehlich]

What is this bot about? ros2/rclcpp#1805 (comment)

[fmauch]

I think that's for integrating the ROS buildfarm for CI tests: http://wiki.ros.org/buildfarm/Pull%20request%20testing