ci: Add commitlint GitHub action to ensure conventional commits with feedback

For more information, see Conventional Commits format in Contribute
https://linux-system-roles.github.io/contribute.html#conventional-commits-format

Signed-off-by: Sergei Petrosian <spetrosi@redhat.com>

.github/workflows/commitlint.yml

@@ -0,0 +1,44 @@
+name: Commitlint
+on:  # yamllint disable-line rule:truthy
+  pull_request:
+    types:
+      - opened
+      - synchronize
+      - reopened
+      - edited
+  merge_group:
+    branches:
+      - main
+    types:
+      - checks_requested
+permissions:
+  contents: read
+jobs:
+  commit-checks:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+
+      - name: Install conventional-commit linter
+        run: npm install @commitlint/config-conventional @commitlint/cli
+
+      # Finding the commit range is not as trivial as it may seem.
+      #
+      # At this stage, git's HEAD does not refer to the latest commit in the
+      # PR, but rather to the merge commit inserted by the PR. So instead we
+      # have to get 'HEAD' from the PR event.
+      #
+      # One cannot use the number of commits
+      # (github.event.pull_request.commits) to find the start commit
+      # i.e. HEAD~N does not work, this breaks if there are merge commits.
+      - name: Run commitlint on commits
+        run: >-
+          npx commitlint --from '${{ github.event.pull_request.base.sha }}'
+          --to '${{ github.event.pull_request.head.sha }}' --verbose
+
+      - name: Run commitlint on PR title
+        run: >-
+          echo '${{ github.event.pull_request.title }}' |
+          npx commitlint --verbose