Add e2e tests that test just the build process

[dario-piotrowicz]

When applications are build using the adapter there are a few things that can happen in the terminal:

• some prompts (e.g. for creating missing open-next and wrangler config files)
• logs (e.g. workers saved at: )
• build errors occur (e.g. getCloudflareContext being used in an SSG'd route)

These things can't be tested in our playwright e2es since they simply rely on a preview command and test the application's functionalities, so ideally we should create a new set of "lower level" e2es that can test the build aspect of the adapter itself.

Additionally with this we can also test that files have been correctly saved onto the filesystem (e.g. handler.mjs.meta.json).

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Original conversation: #330 (review)