LogWriter: On Windows opening the output stream fails when the folder are not created before

Only on windows: VirtualFluids_GPU/Output/LogWriter line 46 fails when fname contains a filepath (e.g. ./output/abcd.log) and the folder does not exist at that time.

When addressing this issue, the following should be considered:

• as we having a new logger, the new one should be used. (https://git.rz.tu-bs.de/irmb/VirtualFluids_dev/-/issues/19)
• instead of handling paths and files as std::string we should move to std::filesystem
• when the LogWriter should still be used, it would be better to not throw a std::string but a std::runtime_error here.

/cc @aileen.brendel /cc @m.schoenherr /cc @a.wellmann