Add an improved design of main Plugin pages

[anna-geller]

Description

When new users navigate to plugin parent pages, those pages are by default quite empty. We display content only when you click on a given task.

Maybe we can find a way to instead show a Table of Contents at the top listing all Tasks, Triggers and Task Runners per plugin, and then automatically expand/show all plugins directly to avoid this page being so empty:

@Nico-Kestra, a design challenge for you 💪 no urgency on this, it's just something worth exploring when you have some downtime