Add `normalizeTrailingNewlines` to the TESTed docs

[jorg-vr]

This was introduced here: dodona-edu/universal-judge#488

Should for example be added here: https://docs.dodona.be/nl/references/tested/dsl/#configuratieopties

[niknetniko]

It should then probably also be mentioned in this section: https://docs.dodona.be/nl/references/tested/dsl/#regeleindes-voor-tekstuele-resultaten