Renamed maintenance mode page to better reflect new content (SharePoint#1163)

Author: waldekmastykarz

docs/general-development/modern-pages-maintenance-mode.md renamed to docs/general-development/client-side-web-parts-maintenance-mode.md

@@ -1027,7 +1027,7 @@
   - name: Use the site collection app catalog
     href: general-development/site-collection-app-catalog.md
   - name: Maintenance mode for client-side web parts
-    href: general-development/modern-pages-maintenance-mode.md
+    href: general-development/client-side-web-parts-maintenance-mode.md
   - name: Set up and configure SharePoint Workflow Manager
     href: general-development/set-up-and-configure-sharepoint-workflow-manager.md
   - name: SharePoint Server Application Lifecycle Management