[FEATURE] Calcite Engine Framework: Basic aggregation integration

[LantaoJin]

Is your feature request related to a problem?
Framework work of the development feature of Calcite Engine.

What solution would you like?
PPL basic Aggregation in Calcite should work (at least 1 agg function)

[andy-k-improving]

@LantaoJin How you foresee the deliverable be like?
In the sense that are we going to expect phased release, with something similar to below:

• Phase-1: In-memory aggregation
• Phase-2: Leverage [FEATURE] Calcite Engine Framework: Enable OpenSearch Pushdown (DSL) #3309 to pushdown aggregation to OpenSearch.

Or we will only release this feature when all aggregations being supported by OpenSearch natively (DSL), and have all aggregation-related query fallback to v2 engine or even legacy engine until this is done?

[LantaoJin]

@LantaoJin How you foresee the deliverable be like? In the sense that are we going to expect phased release, with something similar to below:

• Phase-1: In-memory aggregation
• Phase-2: Leverage [FEATURE] Calcite Engine Framework: Enable OpenSearch Pushdown (DSL) #3309 to pushdown aggregation to OpenSearch.

Or we will only release this feature when all aggregations being supported by OpenSearch natively (DSL), and have all aggregation-related query fallback to v2 engine or even legacy engine until this is done?

Issue named with prefix "Calcite Engine Framework:" only contains fundamental code which ensure basic aggregation operators could work with calcite engine. Notice the push down task #3309 is a Framework task as well. So when both this issue and #3309 are completed, some of aggregations (for example, sum, avg, count) are verified that they could be executed in Calcite engine with pushdown functionality.

When all framework tasks completed, we will start to merge this feature branch to main and create issues for other gaps which not be involved in framework tasks, for example, we won't implement percentile agg in framework part.