fix: middleware not returning response with new NextResponse

[james-elicx]

This PR does the following:

• Modifies the middleware handling to check for the x-middleware-next header and act as follows:
  • If the header exists, remove it and continue as normal.
  • If the header does not exist, and there was no rewrite or location header, this means the middleware response should be the final response we return to the client.
    • Therefore, update the final response body and status.
• Changes the middleware error check to only be for status 500 which is what occurs when an error is thrown in a middleware func.
• Checks if a response body was set during middleware processing and if so, bails out of routing and also uses it when returning a response to the client.
• Adds a test for the new logic.

fixes #283

[changeset-bot]

🦋 Changeset detected

Latest commit: b0f3973

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@cloudflare/next-on-pages	Patch

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[github-actions]

🧪 A prerelease is available for testing 🧪

You can install this latest build in your project with:

npm install --save-dev https://prerelease-registry.devprod.cloudflare.dev/next-on-pages/runs/5176331788/npm-package-next-on-pages-284

Or you can immediately run this with npx:

npx https://prerelease-registry.devprod.cloudflare.dev/next-on-pages/runs/5176331788/npm-package-next-on-pages-284

[dario-piotrowicz]

Awesome, thanks a lot @james-elicx 😃

(sorry for the very late review 😓)

Before merging, could you please add a changeset? 🙂