chore: Add SonarCloud support (#949)

Author: meltsufin

gapic-generator-java/.github/workflows/sonar.yaml

@@ -0,0 +1,36 @@
+name: SonarCloud Build
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    types: [opened, synchronize, reopened]
+jobs:
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0  # Shallow clones should be disabled for a better relevancy of analysis
+      - name: Set up JDK 11
+        uses: actions/setup-java@v1
+        with:
+          java-version: 11
+      - name: Cache SonarCloud packages
+        uses: actions/cache@v1
+        with:
+          path: ~/.sonar/cache
+          key: ${{ runner.os }}-sonar
+          restore-keys: ${{ runner.os }}-sonar
+      - name: Cache Maven packages
+        uses: actions/cache@v1
+        with:
+          path: ~/.m2
+          key: ${{ runner.os }}-m2-${{ hashFiles('**/pom.xml') }}
+          restore-keys: ${{ runner.os }}-m2
+      - name: Build and analyze
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}  # Needed to get PR information, if any
+          SONAR_TOKEN: ${{ secrets.SONAR_TOKEN }}
+        run: mvn -B verify org.sonarsource.scanner.maven:sonar-maven-plugin:sonar -Dsonar.projectKey=googleapis_gapic-generator-java -Dsonar.organization=googleapis -Dsonar.host.url=https://sonarcloud.io