improve find to get more fields from lookups

[marcusdemoura]

When querying the scope of lookups is very limited
could be possible to list the field inside plan and konecty makes the lookup:

fields: ['code', 'plan.permissions', 'plan.expiration']

{
  _id: 'sample-1',
  plan: {
     _id: 'sample-2-plan',
     code: 123,
     name: 'Sample plan'
     permissions: ['permission-1', 'permission-2'],
     expiration: date
  }
}

at least the SDK could abstract the secondary queries.