Move the `package.nix` file from `pkgs/by-name/on/onevpl-intel-gpu` to
`pkgs/by-name/vp/vpl-gpu-rt`. Add an `onevpl-intel-gpu` alias for backwards
compatability.
Intel has merged the `oneapi-src` GitHub organization into the `intel`
namespace. `oneVPL-intel-gpu` has been renamed to `vpl-gpu-rt` as part of
this move. The repo at https://github.com/oneapi-src/oneVPL-intel-gpu now
redirects to https://github.com/intel/vpl-gpu-rt.
