Update nvhpc template and instructions

[fmahebert]

I was able to follow the nvhpc instructions if exactly re-creating the environment used by @climbfuji and I for original testing.

• Ubuntu 22.04
• spack-stack on commit 34bfda12d16a5ddc1a4a50d2f6bb1a52a846138d — soon after v1.7, commit adds nvhpc instructions
• nvhpc sdk 24-3

But when I try with newer Ubuntu, newer nvhpc, or newer spack-stack, the concretizations or builds fail.

As a first step, I'd like to support a more recent spack-stack version, so I will try to update the nvhpc template to mimic any changes to the underlying mpas-jedi template.

[fmahebert]

If compatible with spack-stack workflow, please assign this to me, and add the "INTERFACE" label (in addition to any other labels useful for the spack-stack team)