Improve upgrade documentation

Thanks for opening an issue for something you think could be improved.

However it is too much effort to maintain a second changelog when there is one already as part of each release note → .

The release notes contain mostly automatic content, but sometimes also some handcrafted information.
If you want to see the automatic content for the changes spanning between several versions you can use the same tool used to generate the changelog for each version: https://drupal-mrn.dev/

That said config_filter has been extremely stable and not much has needed to change in the last couple of years.