currently medium path can be set using variables specified in OperatingSystem::interpolate_medium_vars().
they are:

• arch
• major
• minor
• version
• release

This allows the same path format for various combinations of the above params [except #11019]

But often a user wants to have the same path structure in several sites, so that I could specify:

http://download.$site.example.com/path/to/$arch/$major.$minor/$version-$release

this allows to have the same structure across sites/organizations

This feature will require to calculate current operating system's site, and extrapolate it in OperatingSystem::interpolate_medium_vars()