Use blasfeoConfig.cmake when building with BUILD_WITH_BLASFEO=OFF

[traversaro]

This PR is meant more as a proposal/discussion rather then a finished PR.

While removing the patch https://github.com/meco-group/fatrop/pull/18 from the conda-forge recipe of fatrop as 0.0.4 release of fatrop was released, I noticed the only remaining patch was this one.

Basically, blasfeo when installed installs a blasfeoConfig.cmake file, so find_package can be used directly instead of manually calling find_path and find_library and creating an imported target. This works fine in my tests, but if you have any setup with an external blasfeo you want to support, feel free to ask (for example, we could simply add /opt/blasfeo to the PATHS argument of find_package if useful).

fyi @nim65s as he could have an opinion on this based on nix packaging of fatrop.