fix: add appDir path to middleware output path (#75923)
### What?
Add `appDir` path to middleware output path for `nodeMiddleware`
experimental feature
### Why?
For monorepos, the `appDir` is required to copy the `middleware.js` file
to the correct path.
### How?
Add `path.relative(outputFileTracingRoot, distDir),` to the `path.join`
list.
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Co-authored-by: JJ Kasper <jj@jjsweb.site>
