NSFS | Content-type / directory object fixes

[romayalon]

Explain the changes

Issues: Fixed #xxx / Gap #xxx

1. Fixed NSFS should return content-type application/x-directory for dirs #7430
2. Fixed issue raised on slack - https://noobaa.slack.com/archives/C0NSK9ZNE/p1694374090079059
3. Fixed NSFS update content-type from cyberduck fails #7421
4. Today on some flows like override/copy we clean the user. xattr but we shouldn't clean internal xattrs like MD5, we need to merge and have a complete fix for it in - NSFS | moving util functions to native_fs_utils.js file and some cleanup #7463 which contains the initial implementation of user.noobaa. xattr prefix in order to differentiate between user xattr and noobaa internal xattr

Testing Instructions:

• Doc added/updated
• Tests added