Add workflow to detect and report on image vulnerabilities

Signed-off-by: Chip Zoller <chipzoller@gmail.com>

.github/ISSUE_TEMPLATE/VULN-TEMPLATE.md

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+---
+title: Vulnerabilities detected
+labels: security
+---
+High or critical vulnerabilities detected. Scan results are below:
+
+{{ env.RESULTS }}

.github/workflows/report-on-vulnerabilities.yaml

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+name: report-on-vulnerabilities
+on:
+  workflow_dispatch: {}
+  schedule:
+    - cron: '23 2 * * *' # Every day at 02:23
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: ${{ github.repository }}
+jobs:
+  scan:
+    runs-on: ubuntu-20.04
+    permissions:
+      contents: read
+    outputs:
+      results: ${{ steps.parse-results.outputs.results }}
+    steps:
+    - name: Scan for vulnerabilities
+      uses: aquasecurity/trivy-action@d63413b0a4a4482237085319f7f4a1ce99a8f2ac # v0.7.1 (Trivy v0.31.2)
+      with: 
+        image-ref: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:latest
+        format: json
+        ignore-unfixed: false
+        severity: HIGH,CRITICAL
+        output: scan.json
+
+    - name: Parse scan results
+      id: parse-results
+      continue-on-error: true
+      run: |
+        VULNS=$(cat scan.json | jq '.Results[] | has("Vulnerabilities")')
+        if echo $VULNS | grep -q 'true'; then
+          echo "Vulnerabilities found, creating issue"
+          echo ::set-output name=results::$(cat scan.json)
+        else
+          echo "No vulnerabilities found, halting"
+          echo ::set-output name=results::$(echo nothing)
+        fi
+
+    - name: Upload vulnerability scan report
+      uses: actions/upload-artifact@3cea5372237819ed00197afe530f5a7ea3e805c8 # v3.1.0
+      if: contains(steps.parse-results.outputs.results, 'SchemaVersion')
+      with:
+        name: scan.json
+        path: scan.json
+        if-no-files-found: error
+
+  open-issue:
+    runs-on: ubuntu-latest
+    if: contains(needs.scan.outputs.results, 'SchemaVersion')
+    needs: scan
+    steps:
+      - uses: actions/checkout@v3
+      - name: Download scan
+        uses: actions/download-artifact@fb598a63ae348fa914e94cd0ff38f362e927b741 # v3.0.0
+        with:
+          name: scan.json
+
+      - name: Set scan output
+        id: set-scan-output
+        run: echo ::set-output name=results::$(cat scan.json)
+
+      - uses: JasonEtco/create-an-issue@v2
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          RESULTS: ${{ steps.set-scan-output.outputs.results }}
+        with:
+          filename: .github/VULN_TEMPLATE.md