tools/cam: Start to add the testing tools for CAM

Create a directory for testing tools arond CAM. These are snippets of
what will eventually be camio. At the moment, it was written using fbt
traces. This is OK, but fragile, so they need to be re-written with the
cam provider. cam_all_but_scsi.d is the first step. It shows how to do
this with the new cam dtrace provider.

Sponsored by: Netflix
Reviewed by: adrian
Differential Revision: https://reviews.freebsd.org/D54472