ci: add gitleaks scanning workflow and custom rules (#142)

.github/workflows/gitleaks.yml

@@ -0,0 +1,28 @@
+name: Gitleaks
+
+on:
+  pull_request:
+    branches: [main]
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  gitleaks:
+    # Forked pull_request runs do not receive repository/org secrets except GITHUB_TOKEN.
+    if: ${{ github.event_name != 'pull_request' || !github.event.pull_request.head.repo.fork }}
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+        with:
+          fetch-depth: 0
+
+      - uses: gitleaks/gitleaks-action@ff98106e4c7b2bc287b24eaf42907196329070c7 # v2.3.9
+        env:
+          # GITHUB_TOKEN is provided automatically by GitHub Actions.
+          # GITLEAKS_KEY must be configured as a repository secret.
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GITLEAKS_LICENSE: ${{ secrets.GITLEAKS_KEY }}