Allow extending export conditions

[pi0]

nuxt/nuxt#13138

@danielroe https://nodejs.org/api/packages.html#resolving-user-conditions
currently probably only production and development fall into the category of conditions we'd support out-of-the-box, but the capacity to add more or customise them seems useful

Currently, we do use default module node import and I think it is a viable default but allowing to extend woulnd't be a bad idea either