Add GH action to check DCO

Signed-off-by: Stanislav Bogatyrev <stanislav@nspcc.ru>

.github/workflows/dco.yml

@@ -0,0 +1,21 @@
+name: DCO check
+
+on:
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  commits_check_job:
+    runs-on: ubuntu-latest
+    name: Commits Check
+    steps:
+    - name: Get PR Commits
+      id: 'get-pr-commits'
+      uses: tim-actions/get-pr-commits@master
+      with:
+        token: ${{ secrets.GITHUB_TOKEN }}
+    - name: DCO Check
+      uses: tim-actions/dco@master
+      with:
+        commits: ${{ steps.get-pr-commits.outputs.commits }}