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.

Consequently, we also drop the docs/news folder and its content and
adjust the PR template.

.github/workflows/release.yml

@@ -0,0 +1,15 @@
+name: "Create GitHub release"
+
+on:
+  push:
+    tags:
+      - "v*"
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Upstream release
+        uses: osbuild/release-action@main
+        with:
+          token: "${{ secrets.GITHUB_TOKEN }}"