Switch to simple upstream releases

This commit changes our release process from the model of having a
release commit (and pull request) which also updated the NEWS.md file
and bumped the versions in the osbuild.spec and setup.py files to simply
pushing a tag.

After the tag (containing the release notes) is pushed, a GitHub
composite action is triggered that creates a GitHub release with the
contents of the git release tag. Furthermore the bumping of the version
number now always has to happen directly after a release to avoid having
to push a(n untested) commit to main for the release and this is also
handled by the GitHub composite action.

Finally packit pushes directly to dist-git now on pushing the release
tag, so no pull-request needs to be reviewed and merged anymore.

.packit.yaml

@@ -14,6 +14,7 @@ upstream_tag_template: v{version}
 actions:
   get-current-version: bash -c "git describe --tags --abbrev=0 | sed 's|v||'"
 
+create_pr: false
 jobs:
 - job: copr_build
   trigger: pull_request