[cmake] Introduce `Findryml.cmake` file to detect RapidYAML
[cmake] Introduce `Findryml.cmake` file to detect RapidYAML

The `rapidyml` library is a completely optional dependency of RooFit.

olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root