ci(lint): add shell linter - Differential ShellCheck

It performs differential ShellCheck scans and reports results directly on GitHub.

documentation: https://github.com/redhat-plumbers-in-action/differential-shellcheck

Signed-off-by: Jan Macku <jamacku@redhat.com>

.github/workflows/differential-shellcheck.yml

@@ -0,0 +1,36 @@
+name: Differential ShellCheck
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+permissions:
+  contents: read
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+
+    permissions:
+      security-events: write
+
+    steps:
+      - name: Repository checkout
+        uses: actions/checkout@v4
+        with:
+          # Differential ShellCheck requires full git history
+          fetch-depth: 0
+
+      - id: ShellCheck
+        name: Differential ShellCheck
+        uses: redhat-plumbers-in-action/differential-shellcheck@v5
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+
+      - if: always()
+        name: Upload artifact with ShellCheck defects in SARIF format
+        uses: actions/upload-artifact@v4
+        with:
+          name: Differential ShellCheck SARIF
+          path: ${{ steps.ShellCheck.outputs.sarif }}