ci: Add conventional commit check to Tekton linter

* Added a new script step (`conventional-commits`) to the Tekton
  linter pipeline (`.tekton/linter.yaml`).
* Validated the format of the latest commit message using a regex check
  against the Conventional Commits standard.
* Failed the pipeline run if the commit message did not conform to the
  specification.
* Aimed to improve commit history clarity and enable automated changelog
generation.

Signed-off-by: Chmouel Boudjnah <chmouel@redhat.com>

Author: chmouel

.tekton/linter.yaml

@@ -77,6 +77,32 @@ spec:
                 pip3 install gitlint
                 gitlint --commit "$(git log --format=format:%H --no-merges -1)" --ignore "Merge branch"
 
+            - name: conventional-commits
+              displayName: "conventional commit check"
+              image: registry.access.redhat.com/ubi9/python-312
+              workingDir: $(workspaces.source.path)
+              script: |
+                set -x
+                git config --global --add safe.directory /workspace/source
+                base_sha="{{ body.pull_request.base.sha }}"
+                # make sure we have a conventional commit
+                invalid_commits=0
+                while read -r commit_msg; do
+                  if ! echo "$commit_msg" | grep -E -q '^(feat|fix|docs|style|refactor|perf|test|build|ci|chore|revert)(\([a-z0-9-]+\))?:'; then
+                    echo "ERROR: Found commit message that does not follow conventional commit format:"
+                    echo "$commit_msg"
+                    invalid_commits=$((invalid_commits + 1))
+                  fi
+                done < <(git log "${base_sha}..HEAD" --format=format:%s)
+
+                if [ $invalid_commits -gt 0 ]; then
+                  echo "ERROR: $invalid_commits commit(s) do not follow conventional commit format."
+                  echo "Expected format: type(scope): description"
+                  echo "Types: feat, fix, docs, style, refactor, perf, test, build, ci, chore, revert"
+                  echo "See: https://www.conventionalcommits.org/en/v1.0.0/#summary"
+                  exit 1
+                fi
+
             - name: yamllint
               displayName: "YAML Linter"
               image: cytopia/yamllint