Excluding certain app router pages from a build

[rustyx]

I have some mock APIs under /api which are used only during development because in production the APIs are implemented in Go. So when I build the (static) site, I always delete them from the output folder. This works to a degree - due to the fact I'm building a static site, I can't use many features in my mocks, such as request.url, which really restricts the functionality of the mocks.

Hence hereby a request to please add a way to exclude pages from next build, while keeping them in next dev.