2.0.x backport of: Make book child content-type configurable per enabled book content-type

Problem/Motivation

We are unable to upgrade to Drupal 11.2.5 at this time due to various reasons. Currently we're on Drupal 11.1.8.
We need the said functionality provided by 3.0.x that was added in:
✨ Make book child content-type configurable per enabled book content-type Postponed

Proposed resolution

See MR

Remaining tasks

Review MR and test it.

User interface changes

See
✨ Make book child content-type configurable per enabled book content-type Postponed

API changes

Some changes to the book.settings.yml

Data model changes

N/A