Add rapier-debug-render feature

[jeyum2]

Provide features to enable rapier/debug-render when implementing custom debug render instead of bevy's

[Vrixyz]

To be sure, this is currently possible by adding explicitly rapier in the dependencies, and activating the feature from it, correct?

This PR allows to add this feature in a more straightforward manner. OK for me :)

[Vrixyz]

To be correct, shouldn´t the rapier dependency not bring that feature by default ?

rapier debug-render feature isn´t enabled by default 👌

[jeyum2]

To be sure, this is currently possible by adding explicitly rapier in the dependencies, and activating the feature from it, correct?

This PR allows to add this feature in a more straightforward manner. OK for me :)

Of course, it works if you add the same version of rapier used by bevy_rapier as a dependency, but if you use a different version, there's a risk of unexpected behavior.
To prevent this and keep consistency, I think it would be better for bevy_rapier to export the debug-render features.