fix manifest load errors when using assetPrefix (#55416)
### What?
`_devPagesManifest.json` and `_devMiddlewareManifest.json` will fail to load when using an asset prefix. In conjunction with i18n, this causes the app to get caught in an infinite load loop.
### Why?
We're expecting these paths to be exact matches but when there's an assetPrefix specified, they won't be matched.
### How?
This copies similar behavior to how we handle [`webpack-hmr`](https://github.com/vercel/next.js/blob/2e2211d27b3f0ff1cff5553453df4cf391996163/packages/next/src/server/lib/router-server.ts#L681) by doing a partial match on the URL when serving it
Closes NEXT-1618
Fixes #55389
