Identifying empty/blank repositories generated from repository templates

### Is your feature request related to a problem?

Hi! My OSPO is interested in using this action to assist with our repository archival practices. We are building tools to identify repositories that are candidates for archival and plan to use this workflow to assist us in our work of reviewing contents of a repository.

Currently, the workflow is able to identify repos that are empty or README-only. My organization also creates repositories from template repos. It would be valuable if the workflow could detect repositories generated from a template that have no subsequent changes — treating them as effectively blank/empty.

### Describe the solution you'd like

We would like a new feature where the workflow could detect repositories generated from a template that have no subsequent changes — treating them as effectively blank/empty. Maybe this can be done by diffing the candidate repo against the template repo and seeing if there are any meaningful changes

### Describe alternatives you've considered

- Review the commit history. If the repo has 1-2 commits (either an initial commit or template generation commit), this is a signal that it is most likely blank

### Additional context

I'm happy to work on this if it aligns with the project's direction. Just wanted to get your thoughts before diving in!