We should add a $match expression that performs the equivalent of dot product, cosine similarity and euclidean distance functions in mongod, including with secondary indexes on those embedding fields.

In recent projects (prefix/suffix/substring FLE) in which we've added new expressions into MQL, we've decided to restrict new expressions to the aggregation language instead of adding to the $match language as well. We may want to follow suit in this ticket and only add aggregation expressions which have to be used within a $expr in a $match clause.