Unpopular feature request: add costmap source to collision monitor

[tonynajjar]

Feature request

Feature description

I know the collision monitor bypasses the costmap on purpose for faster response but for my application I care less about faster response and more about leveraging the persistence of some of the costmap layers because I lack a 360 degrees perception coverage.
So I'm proposing a CM source that does collision-checking against a costmap it subscribes to.
What do you think?

Implementation considerations

[SteveMacenski]

I'd merge a PR as long as the documentation in the readme and website warned against doing it for the reasons you know about (but that you can if needed)