Linux installers should install manpages to correct location

Installer infra requires `Manpage` items to be set, in the installer project. However those get packaged and installed to `/usr/share/doc`, which is not a correct location - https://github.com/dotnet/arcade/blob/a9ef86690ac8eb6d87f4f47b176ec2b15d3057e3/src/Microsoft.DotNet.Build.Tasks.Installers/build/installer.build.targets#L155-L157

It appears that there are several ways to package and install manpages, and they should most likely be installed ot `/usr/share/man`. This is still TBD.