[add] workflow for pull req

.github/workflows/pull-request.yml

@@ -0,0 +1,81 @@
+name: Merge request pipeline
+
+on:
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  checkstyle:
+
+    runs-on: ubuntu-latest
+    container:
+      image: maven:3.8.5-openjdk-17
+    steps:
+      -
+        name: Checkout code
+        uses: actions/checkout@v4
+
+      -
+        name: Run checkstyle w/ Gradle
+        run: ./gradlew checkstyleMain
+
+      - 
+        name: Upload a Build Artifact
+        uses: actions/upload-artifact@v4.6.0
+        with:
+          name: checkstyle-report
+          path: build/reports/checkstyle/main/checkstyle.xml
+  
+  test:
+
+    runs-on: ubuntu-latest
+    container:
+      image: maven:3.8.5-openjdk-17
+    steps:
+      -
+        name: Checkout code
+        uses: actions/checkout@v4
+      -
+        name: Run tests w/ Gradle
+        run: ./gradlew test
+
+  build:
+
+    runs-on: ubuntu-latest
+    container:
+      image: maven:3.8.5-openjdk-17
+    steps:
+      -
+        name: Checkout code
+        uses: actions/checkout@v4
+
+      -
+        name: Run build w/o tests
+        run: ./gradlew build -x test
+
+  docker:
+
+    runs-on: ubuntu-latest
+
+    steps:
+        - 
+          name: Checkout the code from main branch
+          uses: actions/checkout@v4
+
+        - 
+          name: Login to Docker Hub
+          uses: docker/login-action@v3
+          with:
+            username: ${{ vars.DOCKERHUB_USERNAME }}
+            password: ${{ secrets.DOCKERHUB_PASSWORD }}
+        
+        -
+          name: Set up Docker Buildx
+          uses: docker/setup-buildx-action@v3.9.0
+
+        - 
+          name: Build and push Docker images
+          uses: docker/build-push-action@v6.13.0
+          with:
+            push: true
+            tags: ${{ vars.DOCKERHUB_USERNAME }}/mr:${{ github.sha }}

.github/workflows/push-on-main.yml

@@ -1,10 +1,11 @@
-name: Create and push docker image to Docker Hub.
+name: Create and push docker image to Docker Hub on "push" event.
 
 on:
   push:
     branches: [ main ]
     
 jobs:
+
   docker:
         
     runs-on: ubuntu-latest