FLEPipeline currently accepts a single encryption schema, as a unique_ptr<EncryptionSchemaTreeNode>. FLEPipeline needs to be modified to accept an EncryptionSchemaMap (i.e map<NamespaceString, EncryptionSchemaTreeNode*>).

We will then need to provide an implementation for propagateSchemaForLookup, which correctly propagates the desired schema for the result of the $lookup "as" array.

As mentioned in the scope and design, we will not support using encrypted fields that are within the "as" array in any operations following the $lookup.

In addition, the following constraints must also be enforced as part of this change:

1. Test the following test cases with both CSFLE and QE schemas
   1. Join fields are both encrypted -> Fail 
   2. Local join field encrypted/foreign join field unencrypted -> Fail
   3. Local join field unencrypted/Foreign join field encrypted -> fail
   4. No encrypted fields used as join field -> Succeed
   5.  
   6. Test that mixing CSFLE & QE schemas is not supported.