Fix user information to include payload returned from identity provider

[hugobarauna]

A user is trying to get identity information from their ZTA provider (Cloudflare, in this case) inside a Livebook app.

Livebook was supposed to put that information inside the payload field of the user struct, but this was not happening.

So, when running Kino.Workspace.app_info() from inside a Livebook multi-session app, this was being returned:

Kino.Workspace.info
%{
  type: :multi_session,
  started_by: %{
    id: "239d3f11-f27c-5de4-bbf7-a8d013e8957e",
    name: "Jake Peralta",
    source: :zta,
    payload: nil,
    email: "[email protected]"
  }
}

Notice how payload was nil. ☝️

With this PR, this is now being returned:

Kino.Workspace.info
%{
  type: :multi_session,
  started_by: %{
    id: "239d3f11-f27c-5de4-bbf7-a8d013e8957e",
    name: "Jake Peralta",
    source: :zta,
    payload: %{
      "aud" => ["a8455c4c579173c8f0cc1fc010f740df3f1ccc7209ef32"],
      "country" => "US",
      "email" => "[email protected]",
      "exp" => 17334,
      "iat" => 17334,
      "identity_nonce" => "Ye7i5ZHbI",
      "iss" => "https://99.cloudflareaccess.com",
      "nbf" => 1733488,
      "sub" => "239d3f11",
      "type" => "app"
    },
    email: "[email protected]"
  }
}

[github-actions]

Uffizzi Preview deployment-58894 was deleted.