configure-projects: set build_access_level to private
I was going through policy stuff here:
https://www.mediawiki.org/wiki/GitLab/Policy#Permissions
...and noticed we'd written this:
The "Pipelines" setting in public namespaced projects should be set to "Only Project Members". This ensures that only project members with Reporter privileges are able to run tests on a particular project.
I believe that's what's now under Project -> Settings -> Visibility, project features, permissions -> CI/CD. I'm not totally sure what effect this has, so I guess we'll need to experiment here, and may want to make it optional on a per-project basis.
This also makes the project settings updates only do a single write per changed project.
The project configuration stuff should be rolled into the settings
CLI
elsewhere in this repo, but I'll save that for a later MR.