Add prettier for formatting

[eidottermihi]

We could add prettier as devDependency to ensure proper formatting, e.g. including a prettier --check on build time.

This would need some more docs for developers/contributors on how to:

• properly format their contributions (e.g. running something like npm run prettier:format before committing)

[klml]

@eidottermihi is there a config possibility to config prettier? (I would prefer __Contributions__ befor **Contributions**)

[eidottermihi]

Prettier itself is very "opinionated" and therefore only has a handful options, for those we are using the it@M default config defined in https://github.com/it-at-m/itm-prettier-codeformat/blob/main/src/index.json

For __Contributions__ vs **Contributions** - i think this cannot be configured as there is no option for this: https://prettier.io/docs/en/options