Add github workflow to build and check the code coverage

.github/workflows/main.yml

@@ -0,0 +1,35 @@
+name: Eventeum CI
+
+on:
+  push:
+    branches: [ "master" ]
+  pull_request:
+    branches: [ "master" ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Set up JDK 21
+        uses: actions/setup-java@v3
+        with:
+          java-version: '21'
+          distribution: 'openjdk'
+          cache: maven
+
+      - name: Build with Maven
+        run: mvn clean package
+
+      - name: Run tests
+        run: mvn verify
+
+      - name: Check Coverage
+        run: |
+          COVERAGE=$(cat coverage/target/site/jacoco-aggregate/index.html | grep -o 'Total.*[0-9]\{1,3\}%' | grep -o '[0-9]\{1,3\}%' | head -1 | sed 's/%//')
+          if [ "$COVERAGE" -lt 25 ]; then
+            echo "Coverage below 25%: $COVERAGE%"
+            exit 1
+          fi