Support `spack-packages` to `access-spack-packages`, add `upstream-spack-packages` input

[CodeGat]

References ACCESS-NRI/access-spack-packages#295

Background

Spack has split out their builtin package repo from spack core to it's own spack/spack-packages repository. We want a fork of this repository for our own modifications if required, and are thinking of calling it access-nri/upstream-spack-packages.

This means that we have to change the name of our access-nri/spack-packages repository to something like access-nri/access-spack-packages for consistency.

What This Means

We need to accept refs from upstream-spack-packages and access-spack-packages. Whether this means that inputs.spack-packages-ref is kept around for pre-1.0 inputs.spack-refs is yet to be seen.

Potentially, we may need steps specific to pre-1.0/1.0 versions of spack - this will certainly be the case for oci-backed buildcaches for GitHub-hosted CI.

[CodeGat]

Note that it was decided that we will do a major version update for build-ci also, so we can have spack < 1.0 (mostly) on build-ci v2 and spack >= 1.0 on build-ci v3, similar to the rationale behind ACCESS-NRI/build-cd#326