Update develop from release/1.7.0 and rename spack fork branch

Summary

Update develop from release/1.7.0. I reverted the usual changes to the container configs (yamls), .gitconfig and doc/src/conf.py as for every other release.

On top of that, this PR contains the necessary changes following the renaming of the spack fork branch (and default branch in https://github.com/JCSDA/spack), which affect the container configs (yamls) and .gitmodules.

See announcement https://github.com/JCSDA/spack-stack/discussions/1073 for more information on the branch renaming.

Testing

The release branch was tested heavily on all systems and in CI. This PR is tested in CI (see below)

Applications affected

All (but see testing)

Systems affected

All (but see testing)

Dependencies

https://github.com/JCSDA/spack/pull/422 (merged)

Issue(s) addressed

Link the issues addressed or resolved by this PR (use Fixes #??? for fully resolved issues)

Checklist

[x] This PR addresses one issue/problem/enhancement, or has a very good reason for not doing so.
[x] These changes have been tested on the affected systems and applications.
[x] All dependency PRs/issues have been resolved and this PR can be merged.

JCSDA / spack-stack