Add github action to build extension list

.github/workflows/generate.yml

@@ -0,0 +1,37 @@
+name: Generate extension list
+
+on:
+  schedule:
+    - cron: '11 11 * * *'
+  workflow_dispatch: ~
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    env:
+      FILE: extensions.json
+
+    steps:
+      - name: Checkout source code
+        uses: actions/checkout@v2
+
+      - name: Build JSON file
+        run: php ./generate.php
+
+      - name: Setup git
+        run: |
+          git config user.name "GitHub Actions Bot"
+          git config user.email "<>"
+
+      - name: Get changes
+        id: diff
+        run: |
+          DIFF=$(git diff --numstat -- $FILE | wc -l)
+          echo "::set-output name=DIFF::$DIFF"
+
+      - name: Commit changes
+        run: |
+          git add $FILE
+          git commit -m 'Update extension list'
+          git push origin $GITHUB_REF
+        if: steps.diff.outputs.DIFF != 0