No release notes in release created by GitHub workflow

[FroggyFlox]

In our new GitHub workflow creating a new release in this repository upon each rockstor/rockstor-core release, we do not have release notes included.
It is proposed that we use the GitHub's feature automatically generating release notes for each release. This could be done using the --generate-notes flag for gh: https://cli.github.com/manual/gh_release_create.