[proposal] Include release date in artifact JSON manifests

[evan-goode]

I'm working on adding authlib-injector support to a fork of Prism Launcher, and Prism's library system expects release dates for each version of an library. It would be great if this information were available via the API, for example:

$ curl https://authlib-injector.yushi.moe/artifact/51.json
{
  "build_number": 51,
  "version": "1.2.3",
  "release_date": "2023-06-12 02:46:15 +0800",
  "download_url": "https://authlib-injector.yushi.moe/artifact/51/authlib-injector-1.2.3.jar",
  "checksums": {
    "sha256": "d3ec36486b0a5ab5a16069733cd8d749950c2d62e1bdacaf27864b30b92c1c7f"
  }
}

If desired, I can try to work on this myself and submit a PR to this repo and to https://github.com/yushijinhun/authlib-injector.yushi.moe to retroactively add release dates to old releases.