Codebase Server API: `/codebase` — details about the codebase

[hojberg]

A new endpoint for getting general information about the codebase. Metadata is read via the config file.

This will support https://github.com/unisonweb/unison-local-ui/issues/3

Suggested Response Schema

type CodebaseResponse = {
  hash: String, -- "#asdiojw213dq2",
  defaultAuthor: Maybe Author,
  defaultCopyrightHolder: Maybe Author,
  defaultLicense: Maybe License
}

(this was factored out of https://github.com/unisonweb/unison/issues/2172)

❗This is dependent on https://github.com/unisonweb/unison/issues/2205