feat: add local server

[eduardoboucas]

When using Blobs in Netlify Dev, we want to be able to read and write data from a sandboxed store, without affecting production data.

To make that possible, this PR adds a new local server (for Node.js) that offers the same interface as the edge endpoints, except it reads and writes data to local files on a pre-specified location on disk.

By implementing a server with the same interface as the actual backend, we can just use its address as the edgeURL property when creating a store, and the client will work in exactly the same way as if it was connecting to a live server.

For more context and a demo: https://netlify.slack.com/archives/C05DNT7CLFK/p1697446107031849

Part of https://github.com/netlify/pillar-runtime/issues/754.

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[minivan]

NIIIICE!