[ES|QL] AUTO_BUCKET should accept date fields

[not-napoleon]

Description

Currently, AUTO_BUCKET requires you to format your dates to strings, but that's counter intuitive. It should just accept the date directly.

This should work:

| eval bucket_start = (now()- 1 day)
| eval bucket_end = (now())
| eval bucket = auto_bucket(@timestamp, 24, bucket_start, bucket_end)

Currently we need to use something like

| eval bucket_start = date_format((now()- 1 day))
| eval bucket_end = date_format((now()))
| eval bucket = auto_bucket(@timestamp, 24, bucket_start, bucket_end)

[elasticsearchmachine]

Pinging @elastic/es-ql (Team:QL)

[elasticsearchmachine]

Pinging @elastic/elasticsearch-esql (:Query Languages/ES|QL)

[elasticsearchmachine]

Pinging @elastic/es-analytics-geo (Team:Analytics)