feat: add Table of contents (#981)

* chore: add table of contents module

* refactor

* lint

* null check

---------

Co-authored-by: Philipinho <16838612+Philipinho@users.noreply.github.com>

apps/client/src/features/editor/extensions/extensions.ts

@@ -228,4 +228,4 @@ export const collabExtensions: CollabExtensions = (provider, user) => [
       color: randomElement(userColors),
     },
   }),
-];
+];