Introduce coding standards workflow

workflow-templates/coding-standards.properties.json

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+{
+    "name": "Coding standards",
+    "description": "Enforces Doctrine Coding Standard",
+    "iconName": "doctrine-logo",
+    "categories": [
+        "PHP"
+    ],
+    "filePatterns": [
+        "^phpcs\\.xml(?:\\.dist)$"
+    ]
+}

workflow-templates/coding-standards.yml

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+
+name: "Coding Standards"
+
+on: ["pull_request", "push"]
+
+jobs:
+  coding-standards:
+    name: "Coding Standards"
+    runs-on: "ubuntu-20.04"
+
+    strategy:
+      matrix:
+        php-version:
+          - "7.4"
+
+    steps:
+      - name: "Checkout"
+        uses: "actions/checkout@v2"
+
+      - name: "Install PHP"
+        uses: "shivammathur/setup-php@v2"
+        with:
+          coverage: "none"
+          php-version: "${{ matrix.php-version }}"
+          tools: "cs2pr"
+
+      - name: "Cache dependencies installed with Composer"
+        uses: "actions/cache@v2"
+        with:
+          path: "~/.composer/cache"
+          key: "php-${{ matrix.php-version }}-composer-locked-${{ hashFiles('composer.lock') }}"
+          restore-keys: "php-${{ matrix.php-version }}-composer-locked-"
+
+      - name: "Install dependencies with Composer"
+        run: "composer install --no-interaction --no-progress --no-suggest"
+
+      # https://github.com/doctrine/.github/issues/3
+      - name: "Run PHP_CodeSniffer"
+        run: "vendor/bin/phpcs -q --no-colors --report=checkstyle | cs2pr"