support nested group by queries for time bucketed hyper unique aggregations

[ishan8]

Creates a HyperUnique rollup that generates nested group by queries in order to support aggregating a HyperUnique metric with cardinality calculated at a time based granularity and using that in a derived column post aggregation.

I confirm that this contribution is made under the terms of the license found in the root directory of this repository's source tree and that I have the authority necessary to make this contribution on behalf of its copyright owner.

[hiralsp]

@ishan8 can you rebase off master

[pranavbhole]

@ishan8 Can you please rebase this? lets get this in