Add GH workflow to check for security vulnerabilities

Add Github workflow to check for security vulnerabilities using
`cargo audit`.
This workflow was set up to run every Wednesday at 2:00 UTC.

.github/workflows/security_audit.yml

@@ -0,0 +1,14 @@
+name: Security audit
+
+on:
+  schedule:
+    - cron: '0 2 * * WED'
+
+jobs:
+  audit:
+    runs-on: ubuntu-22.04
+    steps:
+      - uses: actions/checkout@v4
+      - uses: rustsec/audit-check@v1.4.1
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}