build: Add GH action to check for DCO (Signed-Off-By)

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

.github/workflows/dco.yaml

@@ -0,0 +1,18 @@
+name: DCO
+on:
+  pull_request:
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python 3.x
+      uses: actions/setup-python@v1
+      with:
+        python-version: '3.x'
+    - name: Check DCO
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      run: |
+        pip3 install -U dco-check
+        dco-check