Pushdown EQL pipes to aggregations where possible

[colings86]

#49627 will implement the pipes logic in the EQL plugin which is needed for stateful EQL queries such as those that use sequences or joins. For EQL queries that are stateless and can be executed in a single search request, there are many cases where pipes can be evaluated using aggregations. We should add logic that detects these cases and pushes down the evaluation of the pipes into the search request.

[elasticmachine]

Pinging @elastic/es-search (:Search/EQL)

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)