DeltaResponseHandler: add depth control

[MIchaelMainer]

Internal customer request.

I would really like an option for controlling the "depth" for which the DeltaResponseHandler goes to add complex objects to the changelist.
For example in members@delta, Each membership added to a group shows up as 2 changes in the changelist. We process up to 500 memberships at a time, which means the changelist can be size 1000 even though we only care about the fact that memberships are added, and rely on DQ to include only the relevant ones. In this case, i'd want changelist to only include ["members@delta"] and that's it .
Something like new DeltaResponseHandler(depth:1) to only include the top level object would be great. Alternatively, only including the top level object for a complex object is fine with us too.
Reference
#58

AB#7173