✨ Feat: checkstyle workflow 작성

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- 관련: #28

.github/workflows/checkstyle.yml

@@ -0,0 +1,36 @@
+name: 🎨 Checkstyle
+
+on:
+  pull_request:
+    branches: [ main ]
+    types: [ opened, synchronize, reopened ]
+
+
+jobs:
+  checkstyle:
+    name: checkstyle
+    runs-on: ubuntu-latest # ubuntu-22.04
+
+    strategy:
+      matrix:
+        java: [ 17 ]
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Set up JDK ${{ matrix.java }}
+        uses: actions/setup-java@v3
+        with:
+          distribution: temurin
+          java-version: ${{ matrix.java }}
+          architecture: x64
+          cache: "gradle"
+
+      - name: Run Checkstyle
+        uses: dbelyaev/action-checkstyle@master
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          reporter: github-pr-review
+          checkstyle_config: ./lint-config/namo-checkstyle-rules.xml
+          level: warning