GA: add phpcpd action

.github/workflows/phpcpd.yml

@@ -0,0 +1,36 @@
+name: PHPCPD
+
+on:
+  pull_request:
+    branches:
+      - develop
+    paths:
+      - '**.php'
+      - '.github/workflows/phpcpd.yml'
+  push:
+    branches:
+      - develop
+    paths:
+      - '**.php'
+      - '.github/workflows/phpcpd.yml'
+
+jobs:
+  build:
+    name: Code Copy-Paste Detection
+    runs-on: ubuntu-latest
+    if: "!contains(github.event.head_commit.message, '[ci skip]')"
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: '8.0'
+          tools: phpcpd
+          extensions: dom, mbstring
+          coverage: none
+
+      - name: Detect duplicate code
+        run: phpcpd src/ --min-lines 35 --exclude src/Database/Migrations/2022-10-20-182737_ShieldOAuth.php