Add missing mkdocs-mermaid2-plugin to GitHub Pages workflow

- Install mkdocs-mermaid2-plugin to fix the 'mermaid2 plugin is not installed' error
- This should resolve the MkDocs build failure in GitHub Pages deployment
- All required dependencies are now included in the workflow

Author: DimaJoyti

.github/workflows/pages.yml

@@ -28,7 +28,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install mkdocs mkdocs-material pymdown-extensions
+        pip install mkdocs mkdocs-material pymdown-extensions mkdocs-mermaid2-plugin
 
     - name: Build documentation
       run: mkdocs build --clean