Workflows: add CodeQL analysis. (#1178)

Although pyocd already uses LGTM, which is the source of the CodeQL engine, the CodeQL GitHub Actions are more integrated into the Actions UI. For the time being both will be used until it's clear if there's duplication and one should be dropped.

.github/workflows/codeql.yaml

@@ -0,0 +1,46 @@
+# Pyocd CodeQL workflow.
+
+name: "CodeQL"
+
+on:
+  push:
+    branches: [ main, develop ]
+  pull_request:
+    # The branches below must be a subset of the branches above
+    branches: [ main, develop ]
+  schedule:
+    - cron: '42 20 * * 6'
+
+jobs:
+  analyze:
+    name: Analyze
+    runs-on: ubuntu-latest
+    permissions:
+      actions: read
+      contents: read
+      security-events: write
+
+    strategy:
+      fail-fast: false
+      matrix:
+        language: [ 'python' ]
+
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v2
+
+    # Initializes the CodeQL tools for scanning.
+    - name: Initialize CodeQL
+      uses: github/codeql-action/init@v1
+      with:
+        languages: ${{ matrix.language }}
+        # If you wish to specify custom queries, you can do so here or in a config file.
+        # By default, queries listed here will override any specified in a config file.
+        # Prefix the list here with "+" to use these queries and those in the config file.
+        # queries: ./path/to/local/query, your-org/your-repo/queries@main
+
+    - name: Autobuild
+      uses: github/codeql-action/autobuild@v1
+
+    - name: Perform CodeQL Analysis
+      uses: github/codeql-action/analyze@v1