Add scheduled scan

.github/workflows/scheduled_scan.yaml

@@ -0,0 +1,35 @@
+name: Scheduled scan
+
+on:
+  schedule:
+    - cron: '0 21 * * 0'
+
+jobs:
+  scan:
+    runs-on: ubuntu-22.04
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+
+      - name: Install yq
+        run: |
+          sudo snap install yq
+
+      - name: Find version to scan
+        run: |
+          image_name="$(yq '.name' rockcraft.yaml)"
+          echo "image_name=${image_name}" >> $GITHUB_ENV
+          version="$(yq '.version' rockcraft.yaml)"
+          echo "version=${version}" >> $GITHUB_ENV
+
+      - name: Run Trivy vulnerability scanner
+        uses: aquasecurity/trivy-action@master
+        with:
+          image-ref: "ghcr.io/canonical/${{env.image_name}}:${{env.version}}"
+          format: 'sarif'
+          output: 'trivy-results.sarif'
+
+      - name: Upload Trivy scan results to GitHub Security tab
+        uses: github/codeql-action/upload-sarif@v2
+        with:
+          sarif_file: 'trivy-results.sarif'