Allow joins on body fields

Massive JS does not support joins in the body level. It would be good to have this feature.

Use case

Schemas

Say I have the following schemas

users

{
  id,
  body: {
    name,
    age,
    etc
  }
}

transactions

{
  id,
  body: {
    type,
    user_id, // Refers to users.id
  }
}

Code

Example code usage that would allow body joins

1

db.users.join({
  transations: {
    type: 'INNER',
    on: {'body.user_id': 'id'}
  }
}).find({})

2

db.users.join({
  transations: {
    type: 'INNER',
    on: {body: {user_id: 'id'}}
  }
}).find({})