Upgrade to Conan 2

[kyllingstad]

This depends on open-simulation-platform/libcosim#747. (Once that PR has been merged, the version specification of the libcosim requirement should be changed so it no longer points to the osp/testing-feature... branch.)

I had to switch from a simple conanfile.txt to a more involved conanfile.py because the "import" functionality has been removed in Conan 2. Initially this seemed like a hassle, but in the end, it turned out to be beneficial:

• We no longer have to maintain the list of imports by hand. Instead, we dynamically iterate over the dependencies list in the generate() method.
• It allowed me to adjust the RPATH of the imported files from within the conanfile, rather than doing it in the GitHub Actions workflow file as before. Thus, people who build locally also get libaries and executables with an appropriate RPATH.

[kyllingstad]

I've just updated this PR a bit to enable the use of CMake presets created by Conan, which is really convenient. I've updated the README and CI workflow accordingly.