Expanding project reporting functionality

@cameronbateman-mo đang làm issue này rồi.

Từ ngày 6/3/2026.

Once finish_milestone.py has been run all the PRs are archived from the project. In order to easily gather statistics about a release its therefore good to gather that information as part of the script. There is currently a short reporting function that prints the number of pull requests by repo to the terminal while running which can be expanded and modified.

Questions:
* What is the best format for storing these statistics? [A spreadsheet was put together for 2026.03.1 to manually record the data before the archiving was done. Follow this principle?](https://metoffice.sharepoint.com/:x:/r/sites/scienceitteam/Shared%20Documents/SSD%20Team/Release%20Notes/2026.03.1%20Stats.xlsx?d=wac715e53533c4b0ab07a6cb55b0009fc&csf=1&web=1&e=i4wvSr)
* Is this functionality only needed after the release (and can therefore be part of finish_milestone.py), or would it be nice to run mid-release to gather information (e.g. for a presentation or meeting) and therefore should be a standalone script that can be called by finish_milestone.py?
* What details need to be gathered? The 2026.03.1 caught assignees, reviewers, repos and labels. Is this all?

Breakdown:
- [ ] In finish_milestone.py modify the report to store the current repository data to a suitable file
- [ ] Update review_project.py so that all details required are extracted from the raw json
- [ ] Add functions to aggregate those statistics nicely (there are routines for counting items but they are limited at the moment)
- [ ] Expand report funtions to cover the extra stats
- [ ] Move report functionality to its own file if wanted
- [ ] Investigate no error being thrown when permissions for archiving are not set correctly for the user of the script.