fix: use custom copy function to ignore extended attributes

[xoxys]

Credits to the author of paperless-ngx/paperless-ngx#3847 for this solution.

Background (ref):

[...] Files in the container root filesystem will have the MCS label set which will allow only this specific container to access these files. The container process itself will have the same MCS label as these files. Files in volumes on the other hand will not have this label as this would prevent file access in case a container is recreated in which case it will have a new category/MCS label which does not match the ones of the files. When a file is created in the container root filesystem outside of a mounted volume, it will get this MCS label assigned. [...] Looking at the documentation of shutil, it seems like there is no way to tell shutil what kind of "extended attributes" should be copied.