[DOCS] Move code snippets into separate files for EXT:rte_ckeditor

Moving the code snippets into separate files has the advantage that
code highlighting of the IDE is used, and errors may be spotted easier.

Additionally, captions are added to the code blocks.

Resolves: #103318
Releases: main, 12.4
Change-Id: Ia11a6de48176f5e8f890fddc68692cde5c7e74b5
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/83300


Tested-by: Lina Wolf <112@linawolf.de>
Reviewed-by: Lina Wolf <112@linawolf.de>
Tested-by: core-ci <typo3@b13.com>