feat(nextjs-mf): added nextjs-ssr-manifest example

[benmarch]

This is a clone of the nextjs-ssr example, but it uses mf-manifest.json instead of remoteEntry.js. Requires changes from this PR: module-federation/core#2726

This requires some CORS config to allow the manifest to be fetched from the browser. I just added the following to the NextJS config in each app, but there are other ways to do it:

// next.config.js

module.exports = {
  headers() {
    return [
      {
        source: '/_next/static/chunks/mf-manifest.json',
        headers: [
          {
            key: 'Access-Control-Allow-Origin',
            value: '*',
          },
        ],
      }
    ]
  },
  //...
}

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