This work should add a new QSN called EqLookupNode with the following data,

• joinFieldLocal - The outer “left” join field.
• joinFieldForeign - The inner “right” join field.
• joinField - The “as” field for the output array field.
• foreignCollection - the foreign collection namespace string
• Additional fields for indexed NLJ (up to EMEA team).

Consider a possible explain format, 

LOOKUP: {
      from: <foreignCollection>,
      as: <joinField>,
      localField: <joinFieldLocal>,
      foreignField: <joinFieldForeign>,
    }