ESQL: push down filters past INLINESTATS for groupings elements only

[astefan]

Description

This concerns https://github.com/elastic/elasticsearch/blob/main/x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/optimizer/rules/logical/PushDownAndCombineFilters.java#L87 rule where filters (or parts of it) could get pushed down past INLINESTATS in certain queries.

Relates to #115311 as well.

[elasticsearchmachine]

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

[astefan]

In the first query below rather than doing the filter after the join actually happened, the left hand-side (FROM employees essentially) can also use the filter for the left hand side only after data has been collected as part of AVG(salary). In the second query below the filter can also be pushed down on the right hand side, as well.

FROM employees 
           | INLINESTATS avg = AVG(salary) BY languages
           | WHERE emp_no > 10050
           | KEEP avg, languages, salary, emp_no

FROM employees 
           | INLINESTATS avg = AVG(salary) BY languages
           | WHERE languages > 2
           | KEEP avg, languages, salary, emp_no

[astefan]

Implemented with #137572