ESQL: Replace grouping by DateFormat with DateTrunc

[kanoshiou]

Optimize date grouping with formatting in ESQL

This PR optimizes the performance of date grouping operations in ESQL by automatically converting DATE_FORMAT in GROUP BY clauses to more efficient DATE_TRUNC operations. The optimization:

• Automatically detects and converts DATE_FORMAT patterns to equivalent DATE_TRUNC intervals
• Moves date formatting from the grouping phase to a subsequent EVAL phase
• Handles timezone and DST transitions correctly
• Supports various time intervals from nanoseconds to years

Example optimization:

FROM test
| STATS avg = AVG(salary) BY date = DATE_FORMAT("yyyy-MM", hire_date)

becomes:

FROM test
| STATS avg = AVG(salary) BY date1 = DATE_TRUNC(1 month, hire_date) 
| EVAL date = DATE_FORMAT("yyyy-MM", date1) 
| KEEP avg, date

Optimized plan:

Project[[avg{r}#7, date{r}#4]]
\_Eval[[$$SUM$avg$0{r$}#21 / $$COUNT$avg$1{r$}#22 AS avg#7, DATEFORMAT([79 79 79 79 2d 4d 4d][KEYWORD],$$DATE_FORMAT(
"yy>$date$0{r$}#20) AS date#4]]
  \_Limit[1000[INTEGER],false]
    \_Aggregate[[$$DATE_FORMAT("yy>$date$0{r$}#20],[SUM(salary{f}#14,true[BOOLEAN]) AS $$SUM$avg$0#21, COUNT(salary{f}#14,true[
BOOLEAN]) AS $$COUNT$avg$1#22, $$DATE_FORMAT("yy>$date$0{r$}#20]]
      \_Eval[[DATETRUNC(P1M[DATE_PERIOD],hire_date{f}#16) AS $$DATE_FORMAT("yy>$date$0#20]]
        \_EsRelation[test][_meta_field{f}#15, emp_no{f}#9, first_name{f}#10, g..]

Closes #114772

[elasticsearchmachine]

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