Add package for mppnccombine-fast

[aidanheerdegen]

We need a spack package for mppnccombine-fast:

https://github.com/coecms/mppnccombine-fast

It is needed for the ACCESS-OM2 configurations

ACCESS-NRI/access-om2-configs#27

As we need to deploy this to vk83 it is likely we'll need to fork to the ACCESS-NRI organisation. I'll defer to @CodeGat if this is necessary, as it will affect where the package gets its source from.