New Rule: Form without event.preventDefault in onSubmit

[karlhorky]

Many students run into the issue of forgetting to use event.preventDefault in their onSubmit, leading to longer debugging sessions

Since we teach to always prevent the default and manually handle the form submission using fetch, we can warn on this

[karlhorky]

Done in https://github.com/upleveled/eslint-plugin-upleveled/releases/tag/v2.1.0 and https://github.com/upleveled/eslint-config-upleveled/releases/tag/v2.3.0