Esql Enable Date Nanos (elastic#117080)

This enables date nanos support as tech preview. Basic operations, like reading values, binary comparisons, and functions that don't care about type should work, but some functions are not yet supported. Most notably, Bucket is not yet supported, although Date_Trunc is and can be used for grouping. See the docs for the full list of limitations.

relates to elastic#109352

Author: not-napoleon

docs/changelog/117080.yaml

@@ -0,0 +1,5 @@
+pr: 117080
+summary: Esql Enable Date Nanos (tech preview)
+area: ES|QL
+type: enhancement
+issues: []

docs/reference/esql/esql-limitations.asciidoc

@@ -25,6 +25,9 @@ include::processing-commands/limit.asciidoc[tag=limitation]
 * `alias`
 * `boolean`
 * `date`
+* `date_nanos` (Tech Preview)
+** The following functions don't yet support date nanos: `bucket`, `date_format`, `date_parse`, `date_diff`, `date_extract`
+** You can use `to_datetime` to cast to millisecond dates to use unsupported functions
 * `double` (`float`, `half_float`, `scaled_float` are represented as `double`)
 * `ip`
 * `keyword` family including `keyword`, `constant_keyword`, and `wildcard`
@@ -50,7 +53,6 @@ include::processing-commands/limit.asciidoc[tag=limitation]
 ** `position`
 ** `aggregate_metric_double`
 * Date/time
-** `date_nanos`
 ** `date_range`
 * Other types
 ** `binary`