[Org Ledger][Export] Include user column

[garyhtou]

Nice to have, but not necessary.

I'd suggest:

• user_id: public id
• user_name
• user_email

[garyhtou]

For the JSON export, nest the keys.

{
  // ... other transaction stuff
  "user": {
    "id": "usr_abc",
    "name": "Gary Tou",
    "email": "[email protected]"
  }
}