Add logs for code evaluation

[jonatanklosko]

This adds extra logs whenever code is evaluated, showing the code. The metadata includes people connected to the session (or in case of app previews, the person who deployed the app).

When running Livebook with new env vars LIVEBOOK_LOG_LEVEL=info LIVEBOOK_LOG_METADATA=request_id,users, the log looks like this:

18:25:46.105 users=[%{id: "awj6fkaaznjy6ydzhb77id2czn3cmejd", name: "Jonatan Kłosko"}] [info] Evaluating code
  Session mode: default
  Code: "# This is a Code cell - as the name suggests that's where the code goes.\n# To evaluate this cell, you can either press the \"Evaluate\" button above\n# or use `Ctrl + Enter` (or Cmd + Enter on a Mac)!\n\nmessage = \"hey, grab yourself a cup of 🍵\""

The user information includes id, name and email (if available), so it's best combined with an identity provider.

[jonatanklosko]

Alternatively we could interpolate it directly, but printing the new lines would make it much more verbose.

[github-actions]

Uffizzi Preview deployment-58675 was deleted.

[josevalim]

One nitpick!

[josevalim]

Doing the inspection here is problematic because if we have JSON logging in the future, then it will be sent as a string instead of a lists of objects in JSON. Maybe we can cross this bridge later but we may need a custom data structure here, so we can implement both JSON and String.Chars protocols.

[jonatanklosko]

@josevalim I also added metadata for plug and lv :)