Improve release metadata

[dsvensson]

When using Dependabot to automatically get PRs for new Flyway releases the PR is a bit void of information compared to other projects:

Comparing this to other projects, there's some room for improvement:

Worth noting that there used to be a bit more information in earlier releases:

Not sure how dependabot pulls this information, but as it's an embedded GitHub feature, it would be valuable if it provided more in-depth information when a PR opens.