Investigate how groups and permissions are assigned to newly created repositories

[lorawoodford]

New groups are created with pre-defined permissions in an after_create callback in the repository model here: https://github.com/archivesspace/archivesspace/blob/v3.3.1/backend/app/model/repository.rb#L46-L127

We can override that via a plugin that will assign the permissions we want to the groups we want. This repo was created to hold a prototype of that plugin.

I also did a little tinkering to see if we could add the same type of CI guardrails around this override that we have for plugins that override views (e.g. https://github.com/Smithsonian/caas_aspace_sova_button). Using the same basic diffing idea, that is working in CI here as well and can be seen on this initial PR: https://github.com/Smithsonian/caas_aspace_group_baselines/actions/runs/12520979093/job/34927417018