[DOCS] Update examples of CKEditor 5 plugin

The changelog now shows a current version
of the timestamp plugin.
In the documentation of EXT:rte_ckeditor,
a typo in the plugin namespace is fixed.
Both examples show the same code.

Resolves: #101971
Releases: main, 12.4
Change-Id: Ic8900bd990717d1887601ddf4ecabebfe78075a4
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/81102


Tested-by: core-ci <typo3@b13.com>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Benjamin Franzke <ben@bnf.dev>
Tested-by: Benjamin Franzke <ben@bnf.dev>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Garvin Hicking <gh@faktor-e.de>