Add GitHub Actions to format Java code

Author: cszach

.github/workflows/code-formatting.yml

@@ -0,0 +1,15 @@
+name: Code formatting
+
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  formatting:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: axel-op/googlejavaformat-action@v3
+        with:
+          args: "--replace"