1. Add a query knob for kMaxHashJoinCollectionSize. Currently, we've hardcoded the value of 100*1024*1024 in the code that selects the physical join algorithm. This should be a configurable knob (both for testing purposes and to let customers to, effectively, fully suppress HJ)
2. Add a query knob that limits the number of records in the foreign collection to be considered for a HJ.
3. Check the storage size of the collection.