[DOCS] Improve example in changelog about tree node labels

Use a full example of an event listener and enclose the RGB value in
quotes. The example also omits named arguments. Additionally, we have
currently no "tsconfig" language in the Sphinx-based rendering,
"typoscript" is used therefore. Also, captions are added for the code
blocks for easier adoption.

Resolves: #103257
Related: #103257
Releases: main
Change-Id: Ifd3bb51352011223470de988e6153252869d982b
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/83184


Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>