Integrate Github codebase visualizer into JuiceFS workflow (#731)

.github/workflows/diagram.yml

+name: Create diagram
+on:
+  workflow_dispatch: {}
+  push:
+    branches:
+      - main
+jobs:
+  get_data:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@master
+      - name: Update diagram
+        uses: githubocto/repo-visualizer@main
+        with:
+          excluded_paths: ".github"
+          output_file: "docs/images/repo-diagram.svg"