Translations update action/script contains hard-coded list of categories

**Short description**: The script/GH action that creates the localised files in the main branch from the translation files in the translation-files branch, has a hard-coded list of categories. As in #155 I changed the category name, its pages now no longer appear translated on the website.

**URL**: e.g. https://antennapod.org/nl/documentation/bugs-first-aid/bug-report

**More info**: https://github.com/AntennaPod/antennapod.github.io/blob/1f824dda426edd8fc6e18d5e660c38db3c10af95/.github/workflows/translation-updates-to-main-repo.yml#L98

We should automatically create a list of categories based on the folders.