add CI security workflow (#668)

Add supports for Datadog static analysis. It checks rules that validates
the GitHub actions are safe and secure.

.github/workflows/datadog-static-analysis.yml

@@ -0,0 +1,21 @@
+on: [push]
+
+name: Datadog Static Analysis
+
+jobs:
+  static-analysis:
+    runs-on: ubuntu-latest
+    name: Datadog Static Analyzer
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v3
+    - name: Check code meets quality and security standards
+      id: datadog-static-analysis
+      uses: DataDog/datadog-static-analyzer-github-action@v1
+      with:
+        dd_api_key: ${{ secrets.DD_STATIC_ANALYSIS_API_KEY }}
+        dd_app_key: ${{ secrets.DD_STATIC_ANALYSIS_APP_KEY }}
+        dd_service: dd-trace-py
+        dd_env: ci
+        dd_site: datadoghq.com
+        cpu_count: 2

static-analysis.datadog.yml

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+rulesets:
+  - sit-ci-best-practices:
+    only:
+      - ".github/workflows"