feat: support editor to show workspace view overview

[Jayaprakash-dev]

I've addressed the issue #4282 by implementing the Workspace folder Overview feature, allowing users to create an outline for workspace folder/sub pages structures using the slash commands /overview or /workspace overview. This facilitates easy navigation in nested document structures.

Screenshot and Demo

https://github.com/AppFlowy-IO/AppFlowy/assets/68953739/cc974dad-7716-427b-a4fe-c7c9f89c01fe

[LucasXu0]

Hey, @Jayaprakash-dev, fyi, the review isn't complete yet. I need to run it locally to test the functionality.