ESQL: INLINESTATS followup

[nik9000]

Description

https://github.com/elastic/elasticsearch/pull/109583 will add support for INLINESTATS, a command to run a STATS and then merge the results into the stream of results. This issue tracks follow up work:

Before GA

• [x] Run logical plan optimization before splitting the phases. See https://github.com/elastic/elasticsearch/pull/109583#discussion_r1683084852
• [x] Allow functions in the grouping position (+union types test with conversion in the grouping position // TODO once inlinestats supports expressions in groups we'll likely need the same sort of extraction here)
• [ ] Address left over comments on https://github.com/elastic/elasticsearch/pull/111690
• [ ] Fix union fields in INLINESTATS - they are allowed now but they produce "fun" error messages and don't work
• [x] Add all phases to the result of profile
• [ ] Allow push down for conditions coming from the EVAL based join. So | INLINESTATS a=AVG(foo) | WHERE foo > a should be able to push the foo > a bit in the second phase. It can't now.
• [ ] Track intermediate request memory usage and lift the 1mb limit.
• [ ] Keep readers open for the second round.
• [ ] Fix the test labeled brokenWhy-Ignore, byConstant-Ignored
• [ ] More shadowing tests
• [ ] Fix INLINESTATS x=MAX(a), x=MIN(a) - shadowingInternal-Ignored
• [ ] Fix shadowingSelfBySelf
• [ ] Fix INLINESTATS in CCS
• [ ] Once we have the above - we should look into pushing the Phased stuff further into physical planning. It'd be nice to, for example, and a SubqueryExec plan that runs like Phased does here. Not sure if physical or logical - but physical feels better. We're doing logical now though.
• [ ] Test with the BUCKET function. Sounds like it doesn't work at the moment.
• [ ] More than one INLINESTATS. see. Note that this might have to do with multiple lookups - that's tracked in https://github.com/elastic/elasticsearch/issues/109353

Evantually

• [ ] Some https://github.com/elastic/elasticsearch/issues/109353