[DOCS] Improve changelog for auto-registration of new ce wizard via TCA

The given migration examples were not really practical, as an integrator
does not return an array, but use either the API for adding a new
content element/plugin, or manipulate the TCA array directly via
`Configuration/TCA/Overrides/tt_content.php` for adding `saveAndClose`
or `defaultValues`. To ease the work for integrators when migrating
to the new options, the examples have been improved.

Additionally, captions for the files have been added to ease grasping
the context of the examples.

Resolves: #104806
Related: #102834
Releases: main
Change-Id: Idc840c611751be79dec475d372c9a2f29d23f32f
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/85860


Tested-by: Garvin Hicking <gh@faktor-e.de>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Garvin Hicking <gh@faktor-e.de>