We are trying to deploy onto a shared Jenkins cluster, and one of the only things that holds us back is the fact that the JIRA site configuration is global and cannot be configured on a folder-by-folder basis.

I would like to be able to configure the JIRA sites on a folder instead of just globally, with the folder ones taking precedence over the global ones.

A good example of this being done already is in the pipeline-model-definition-plugin. The config provider checks the parent folders first (going up the hierarchy), and then the global configuration. I've implemented this on at least one plugin myself and can help out if it's not clear.