let's check the format via some github action

Signed-off-by: Matthieu Gallien <matthieu.gallien@nextcloud.com>

.github/workflows/clang-format.yml

@@ -0,0 +1,12 @@
+name: Clang Format Checker
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+jobs:
+  clang-format-checking:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: RafikFarhad/clang-format-github-action@v2.1.0
+        with:
+          sources: "src/**/*.h,src/**/*.c,src/**/*.cpp,test/**/*.c,test/**/*.cpp,shell_integration**/*.cpp"