Use `page_stats.py` in the build process to output stats about # of pages and redirects

[ftisiot]

What should we add to our content collections?

The file page_stats.py counts the number of articles in devportal and the number of redirects from help.aiven.io It would be cool if we could run it on build to show some human readable stats when we create a PR

Is this something you would work on yourself?

[ ] I plan to open a pull request for this