Improvements to Code Node Explained Page

### Description

I really like the Core Nodes pages. I would like to suggest some improvements:
1. For the Left hand navigation it would be nice to have this list to be expandable. At the top level should be: Common, Function, Network, Parsers, Sequence, Storage. Each one of these the user should be able to expand to see the next level.
2. I would like to use the title 'Node-RED Core Nodes Explained'
3. For the introductory text, it would be nice to for each section description include a link to the section in the left hand side and expand it out.
4. I would move the search bar to the top of the left hand side.

### Epic/Story

_No response_

### Have you provided an initial effort estimate for this issue?

I have provided an initial effort estimate