Add Github action for checking pr code style

.github/workflows/check-pr-style.yml

@@ -0,0 +1,30 @@
+name: Check PR code style
+
+on:
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up JDK 11
+      uses: actions/setup-java@v1
+      with:
+        java-version: 1.11
+    - name: Run java checkstyle
+      uses: nikitasavinov/checkstyle-action@0.3.1
+      with:
+        # Report level for reviewdog [info,warning,error]
+        level: info
+        # Reporter of reviewdog command [github-pr-check,github-pr-review]
+        reporter: github-pr-check
+        # Filtering for the reviewdog command [added,diff_context,file,nofilter].
+        filter_mode: added
+        # Exit code for reviewdog when errors are found [true,false].
+        fail_on_error: false
+        # Checkstyle config file
+        checkstyle_config: minestom_checks.xml