Grid config input paths should be relative to the path of the simona config file

[sebastian-peter]

Looking into simona config files, input paths that are given as relative paths are always relative to the working directory that simona is started in.

https://github.com/ie3-institute/simona/blob/707fc989981b6f9d2bb6d7fc19fcf86710169124/input/samples/vn_simona/vn_simona.conf#L26

https://github.com/ie3-institute/simona/blob/707fc989981b6f9d2bb6d7fc19fcf86710169124/input/samples/vn_simona/vn_simona.conf#L32

This is a bit inconvenient, I think it'd be better to treat these paths as relative to the simona config file. This means, the examples above would turn into:

directoryPath: "fullGrid"

Output paths should still be relative to the working directory.

cc @t-ober @danielfeismann