refactor(ci): change the way releases are automated

[ckipp01]

A lot of users will get Steward PRs that automatically link to the release page of that release. For example with the last release here this linked to https://github.com/com-lihaoyi/requests-scala/releases/tag/0.8.0. The thing is, this page is empty and doesn't tell the user anything. I know it's common in the com-lihaoyi ecosystem to include the changelog in the readme, so maybe we can also automate the release better. This pr changes a couple things:

• Changes the actual github action in control of the release. The one we were using before (https://github.com/actions/create-release) is archived and no longer maintained. This switches to a new one that from what I can tell is the most popular (https://github.com/softprops/action-gh-release).
• Use the generate_release_notes option which will automate generating the release notes by just putting all the commits for this release in there.
• Use append_body to also then link to the changelog in the readme.

This should be a nicer experience for those clicking the link with Steward without changing the way you currently manually do your changelog.