Need a mechanism to specify maintainers for systems and experiments

[pearce8]

Ideally, we should have a maintainer for every system config (e.g., nosite-x86_64) and experiment (e.g., amg2023/cuda). The goals are the same as for Spack maintainers. I did not find a page on maintainers - but Spack's contribution guide is here:

https://spack.readthedocs.io/en/latest/contribution_guide.html