The metadata returned by rc stat does not include Content Type in the same way mc stat does

[krystal1549]

Thank you for adding Metadata to rc stat. However, it is missing the Content Type that is returned in mc stat. This should look like this:

Name : my-bucket/my-file.txt
Date : 2024-03-09 10:00:00 UTC
Size : 1.5 KiB
ETag : d41d8cd98f00b204e9800998ecf8427e
Type : file
Metadata :
Content-Type : text/plain

[overtrue]

Implemented in #48. The fix updates human-readable rc stat output to include Content-Type in the metadata section and restores Type to object kind (file). Verified against rustfs/rustfs:latest using Docker.