Implement FUSE symlink

[radumarias]

specs: https://github.com/libfuse/libfuse/blob/master/include/fuse.h#L385

You need to implement https://github.com/Sherlock-Holo/fuse3/blob/17eae92592c4aab5a9dd30d5b09a92987c0d4823/src/raw/filesystem.rs#L68 in https://github.com/radumarias/rencfs/blob/main/src/mount/linux.rs#L260 and call similar names function from https://github.com/radumarias/rencfs/blob/main/src/encryptedfs.rs#L548 to implement the actual functionality.

How to implement
When creating a symlink to a file you save in the file content in contents folder the path to which it points. When accessing this symlink you will actually forward all operations to the file in the path.

For now allow src to only be file, as it's easier to implement, we'll handle that case in the future. Meaning you can have dir > dir.