Show changelog in release PR description

It would be helpful to show the changelog in the release PR description, to help the reviewers understand what has changed in the release. We could embed the entire changelog contents for the current release, or we could do something simpler like link the section of the changelog for the current release.

The issue does not name a file, test, or entry point. First locate where the release PR description is assembled, then determine whether the current release changelog should be embedded or linked; it is done when reviewers can see the current release's changelog from the PR description.

Written by the indexing model from the issue text.