refactor(v-onboarding-wrapper): convert to script setup

[J-Michalek]

Provide better TS support by allowing the step type to be generic.

In my project I extend the steps with extra properties and want it to be fully types within the slot (as of now it is typed as any).

I converted the component into script setup syntax but the issue arose when I tried to build it - it seems the type generation this project uses is unable to handle the generic type for a prop, not sure how to progress further since I have no knowledge of vue-docgen-web-types or its necessity.

Any help would be much appreciated!