Add OS/Arch information into `oras version`

As per the ORAS diagnose experience proposal, we should include the OS/Arch information in the output of oras version.

oras/docs/proposals/diagnose-experience.md

Line 81 in 5280c67

    
           - Show running environment details of ORAS such as `OS/Arch` in the output of `oras version`. It would be helpful to help the ORAS developers locate and reproduce the issue easier.

Example:

$ oras version

ORAS Version:    1.2.0+Homebrew
Go version:      go1.22.3
OS/Arch:         linux/amd64
Git commit:      xxxxxxxxxxxx
Git tree state:  clean