This change introduces the minimal amount of changes to accomplish the
following:

- Old "book" is now Quick Start
- New book has a initial version (v0.11.0) with one page
- A link which defaults to being hidden has been added to the list of
  links on /learn

- This incorporates changes from 97fef72, which is latest commit on new-book branch
- Smallest amount of changes to get the overall book structure change
- Various styling / minor fixes most probably missing from new-book
  - These can be applied later, right now a lot of conflicts so defer
- Redirects properly setup to go the first section

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>

This is a temporary measure in order to stop Google et al from indexing
the book before a first version been finalized. Pages within the book
won't show up in any search results and can only be accessed by direct
URL access for now.

Taken from summarizing bevyengine#623

Added to the bottom of the Book section list on the left.

- Reads versions from `content/learn/book/versions.toml` so we can start
  working on the book for a new version and have the content in `main`
  without neccessarly publishing it on the website

Pages that been checked to redirect correctly:

https://bevyengine.org/learn/book/introduction/
https://bevyengine.org/learn/book/getting-started/
https://bevyengine.org/learn/book/getting-started/setup/
https://bevyengine.org/learn/book/getting-started/apps/
https://bevyengine.org/learn/book/getting-started/ecs/
https://bevyengine.org/learn/book/getting-started/plugins/
https://bevyengine.org/learn/book/getting-started/resources/
https://bevyengine.org/learn/book/next-steps/
https://bevyengine.org/learn/book/contributing/
https://bevyengine.org/learn/book/contributing/code/
https://bevyengine.org/learn/book/contributing/docs/
https://bevyengine.org/learn/book/troubleshooting/

Everything should redirect properly from:

https://bevyengine.org/learn/book/*

To:

https://bevyengine.org/learn/quick-start/*